<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019ca091-8509-7033-ac72-6caf24ed7e98,g:49aa57d8-843a-42f0-b323-95a00ac8fc9c-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://quantaservices.com/role/CondensedConsolidatedStatementsofEquity" xlink:type="simple" xlink:href="pwr-20260331.xsd#CondensedConsolidatedStatementsofEquity"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/CondensedConsolidatedStatementsofEquity" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019ca091-8713-7eb8-a071-584b3e428a9b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019ca091-8713-72f1-b2a6-54ea1a987ddf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019ca091-8713-7eb8-a071-584b3e428a9b" xlink:to="loc_us-gaap_StatementTable_019ca091-8713-72f1-b2a6-54ea1a987ddf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019ca091-8713-7499-a565-98b55f1eee2c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019ca091-8713-72f1-b2a6-54ea1a987ddf" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019ca091-8713-7499-a565-98b55f1eee2c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019ca091-8713-7499-a565-98b55f1eee2c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019ca091-8713-7499-a565-98b55f1eee2c" xlink:to="loc_us-gaap_EquityComponentDomain_019ca091-8713-7499-a565-98b55f1eee2c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019ca091-8713-753a-90d9-b82a22347e11" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019ca091-8713-7499-a565-98b55f1eee2c" xlink:to="loc_us-gaap_EquityComponentDomain_019ca091-8713-753a-90d9-b82a22347e11" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ParentMember_019ca091-8713-7ee4-8871-f769b1b829e8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ca091-8713-753a-90d9-b82a22347e11" xlink:to="loc_us-gaap_ParentMember_019ca091-8713-7ee4-8871-f769b1b829e8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019ca091-8713-7141-a43b-e70e773c32c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019ca091-8713-7ee4-8871-f769b1b829e8" xlink:to="loc_us-gaap_CommonStockMember_019ca091-8713-7141-a43b-e70e773c32c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019ca091-8713-7a31-bc69-0c1a4e6f274a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019ca091-8713-7ee4-8871-f769b1b829e8" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019ca091-8713-7a31-bc69-0c1a4e6f274a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019ca091-8713-7cb5-8b95-0cd56b32403a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019ca091-8713-7ee4-8871-f769b1b829e8" xlink:to="loc_us-gaap_RetainedEarningsMember_019ca091-8713-7cb5-8b95-0cd56b32403a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019ca091-8713-71a8-b43d-756e9242b8c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019ca091-8713-7ee4-8871-f769b1b829e8" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019ca091-8713-71a8-b43d-756e9242b8c5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_019ca091-8713-789b-820a-2b174a59edb4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019ca091-8713-7ee4-8871-f769b1b829e8" xlink:to="loc_us-gaap_TreasuryStockCommonMember_019ca091-8713-789b-820a-2b174a59edb4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_019ca091-8713-77b2-a4da-b5eeb467dcbf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ca091-8713-753a-90d9-b82a22347e11" xlink:to="loc_us-gaap_NoncontrollingInterestMember_019ca091-8713-77b2-a4da-b5eeb467dcbf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ca091-8713-7b54-b390-9c3f91ddc5cc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ca091-8713-7eb8-a071-584b3e428a9b" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ca091-8713-7b54-b390-9c3f91ddc5cc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019ca091-8713-7634-be76-6204034c3e26" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ca091-8713-7b54-b390-9c3f91ddc5cc" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019ca091-8713-7634-be76-6204034c3e26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019ca091-8713-7525-baca-4a306bf9decd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ca091-8713-7b54-b390-9c3f91ddc5cc" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019ca091-8713-7525-baca-4a306bf9decd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019ca091-8713-7fde-8158-f91032255ad2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ca091-8713-7b54-b390-9c3f91ddc5cc" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019ca091-8713-7fde-8158-f91032255ad2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_NoncontrollingInterestDecreaseFromAcquisitionsMeasurementPeriodAdjustments_019dd011-ab02-7af6-82cf-4973d38756c8" xlink:href="pwr-20260331.xsd#pwr_NoncontrollingInterestDecreaseFromAcquisitionsMeasurementPeriodAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ca091-8713-7b54-b390-9c3f91ddc5cc" xlink:to="loc_pwr_NoncontrollingInterestDecreaseFromAcquisitionsMeasurementPeriodAdjustments_019dd011-ab02-7af6-82cf-4973d38756c8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_019ca091-8713-7c10-8cd6-3278fd6733a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ca091-8713-7b54-b390-9c3f91ddc5cc" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_019ca091-8713-7c10-8cd6-3278fd6733a7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_019ca091-8713-72e2-bd6c-a58cacf222fd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ca091-8713-7b54-b390-9c3f91ddc5cc" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_019ca091-8713-72e2-bd6c-a58cacf222fd" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStockCash_019ca091-8713-7db8-9d69-ca04de3e7418" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendsCommonStockCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ca091-8713-7b54-b390-9c3f91ddc5cc" xlink:to="loc_us-gaap_DividendsCommonStockCash_019ca091-8713-7db8-9d69-ca04de3e7418" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_019ca091-8713-7359-8973-ca41621035a1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ca091-8713-7b54-b390-9c3f91ddc5cc" xlink:to="loc_us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_019ca091-8713-7359-8973-ca41621035a1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_019ca091-8713-7646-9869-1ae9dffd56f5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ca091-8713-7b54-b390-9c3f91ddc5cc" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_019ca091-8713-7646-9869-1ae9dffd56f5" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_019ca091-8713-7753-904f-5cecb8669350" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ca091-8713-7b54-b390-9c3f91ddc5cc" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_019ca091-8713-7753-904f-5cecb8669350" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_019ca091-8713-7257-b550-a81916a4af34" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ca091-8713-7b54-b390-9c3f91ddc5cc" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_019ca091-8713-7257-b550-a81916a4af34" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_019ca091-8713-79af-bde6-8768f366a1fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ca091-8713-7b54-b390-9c3f91ddc5cc" xlink:to="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_019ca091-8713-79af-bde6-8768f366a1fe" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019ca091-8713-73fa-bd11-97482faf493c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ca091-8713-7b54-b390-9c3f91ddc5cc" xlink:to="loc_us-gaap_ProfitLoss_019ca091-8713-73fa-bd11-97482faf493c" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019ca091-8713-7ffb-ae95-f62f4628eb28" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019ca091-8713-7f78-bc15-2e23cca968b3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/RevenueRecognitionandRelatedBalanceSheetAccountsRevenueDisaggregatedbyGeographicLocationandContractTypeDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#RevenueRecognitionandRelatedBalanceSheetAccountsRevenueDisaggregatedbyGeographicLocationandContractTypeDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/RevenueRecognitionandRelatedBalanceSheetAccountsRevenueDisaggregatedbyGeographicLocationandContractTypeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7135-b2f3-68bab9c80d9e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019ca091-8713-7227-9036-a1664227a5bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7135-b2f3-68bab9c80d9e" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019ca091-8713-7227-9036-a1664227a5bd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_019ca091-8713-7fbc-a4fe-eea36dbf548d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerBasisOfPricingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019ca091-8713-7227-9036-a1664227a5bd" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_019ca091-8713-7fbc-a4fe-eea36dbf548d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_019ca091-8713-7fbc-a4fe-eea36dbf548d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerBasisOfPricingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_019ca091-8713-7fbc-a4fe-eea36dbf548d" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_019ca091-8713-7fbc-a4fe-eea36dbf548d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_019ca091-8713-7a47-a00c-7ee69d9010b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerBasisOfPricingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_019ca091-8713-7fbc-a4fe-eea36dbf548d" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_019ca091-8713-7a47-a00c-7ee69d9010b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedPriceContractMember_019ca091-8713-7ad1-8b00-3962fe0649c3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FixedPriceContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_019ca091-8713-7a47-a00c-7ee69d9010b6" xlink:to="loc_us-gaap_FixedPriceContractMember_019ca091-8713-7ad1-8b00-3962fe0649c3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_UnitPriceContractsMember_019ca091-8713-7be6-944b-3bd69769a236" xlink:href="pwr-20260331.xsd#pwr_UnitPriceContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_019ca091-8713-7a47-a00c-7ee69d9010b6" xlink:to="loc_pwr_UnitPriceContractsMember_019ca091-8713-7be6-944b-3bd69769a236" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_CostPlusContractMemberMember_019ca091-8713-7cc9-af63-7e5409c28009" xlink:href="pwr-20260331.xsd#pwr_CostPlusContractMemberMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_019ca091-8713-7a47-a00c-7ee69d9010b6" xlink:to="loc_pwr_CostPlusContractMemberMember_019ca091-8713-7cc9-af63-7e5409c28009" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019ca091-8713-7890-9590-db749072cd0f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019ca091-8713-7227-9036-a1664227a5bd" xlink:to="loc_srt_StatementGeographicalAxis_019ca091-8713-7890-9590-db749072cd0f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019ca091-8713-7890-9590-db749072cd0f_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019ca091-8713-7890-9590-db749072cd0f" xlink:to="loc_srt_SegmentGeographicalDomain_019ca091-8713-7890-9590-db749072cd0f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019ca091-8713-7898-b005-299aa59e21ae" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019ca091-8713-7890-9590-db749072cd0f" xlink:to="loc_srt_SegmentGeographicalDomain_019ca091-8713-7898-b005-299aa59e21ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_019ca091-8713-711f-af6e-e4c85f77956b" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019ca091-8713-7898-b005-299aa59e21ae" xlink:to="loc_country_US_019ca091-8713-711f-af6e-e4c85f77956b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CA_019ca091-8713-7ad7-b6cb-ec25826c918c" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_CA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019ca091-8713-7898-b005-299aa59e21ae" xlink:to="loc_country_CA_019ca091-8713-7ad7-b6cb-ec25826c918c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_AU_019ca091-8713-7c83-a024-de0f5df394e7" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_AU"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019ca091-8713-7898-b005-299aa59e21ae" xlink:to="loc_country_AU_019ca091-8713-7c83-a024-de0f5df394e7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_OtherCountriesMember_019ca091-8713-79cb-b63d-31299fb45d09" xlink:href="pwr-20260331.xsd#pwr_OtherCountriesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019ca091-8713-7898-b005-299aa59e21ae" xlink:to="loc_pwr_OtherCountriesMember_019ca091-8713-79cb-b63d-31299fb45d09" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019ca091-8713-7e1d-ace2-b4ce81379a71" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7135-b2f3-68bab9c80d9e" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019ca091-8713-7e1d-ace2-b4ce81379a71" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_PercentageOfTotalRevenues_019ca091-8713-753c-a25a-b562ec354b73" xlink:href="pwr-20260331.xsd#pwr_PercentageOfTotalRevenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7135-b2f3-68bab9c80d9e" xlink:to="loc_pwr_PercentageOfTotalRevenues_019ca091-8713-753c-a25a-b562ec354b73" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/RevenueRecognitionandRelatedBalanceSheetAccountsAdditionalInformationDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#RevenueRecognitionandRelatedBalanceSheetAccountsAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/RevenueRecognitionandRelatedBalanceSheetAccountsAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019ca091-8713-733e-ba0e-c47e0699ae63" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019ca091-8713-733e-ba0e-c47e0699ae63" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019ca091-8713-7634-afd0-a5cacbf046d8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019ca091-8713-733e-ba0e-c47e0699ae63" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019ca091-8713-7634-afd0-a5cacbf046d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019ca091-8713-7634-afd0-a5cacbf046d8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019ca091-8713-7634-afd0-a5cacbf046d8" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019ca091-8713-7634-afd0-a5cacbf046d8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019ca091-8713-7238-a081-141144975fe2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019ca091-8713-7634-afd0-a5cacbf046d8" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019ca091-8713-7238-a081-141144975fe2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditConcentrationRiskMember_019ca091-8713-7de5-9832-c52838798034" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019ca091-8713-7238-a081-141144975fe2" xlink:to="loc_us-gaap_CreditConcentrationRiskMember_019ca091-8713-7de5-9832-c52838798034" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_019ca091-8713-7de4-a078-de12790bd163" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019ca091-8713-7238-a081-141144975fe2" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_019ca091-8713-7de4-a078-de12790bd163" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019ca091-8713-7c0b-839e-eff50f69783c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019ca091-8713-733e-ba0e-c47e0699ae63" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019ca091-8713-7c0b-839e-eff50f69783c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019ca091-8713-7c0b-839e-eff50f69783c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019ca091-8713-7c0b-839e-eff50f69783c" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019ca091-8713-7c0b-839e-eff50f69783c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019ca091-8713-7ea1-959a-3d0f0cc144f8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019ca091-8713-7c0b-839e-eff50f69783c" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019ca091-8713-7ea1-959a-3d0f0cc144f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_FinancialInstrumentsMember_019ca091-8713-718e-90ec-a166d72e9129" xlink:href="pwr-20260331.xsd#pwr_FinancialInstrumentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019ca091-8713-7ea1-959a-3d0f0cc144f8" xlink:to="loc_pwr_FinancialInstrumentsMember_019ca091-8713-718e-90ec-a166d72e9129" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_019ca091-8713-7360-bfee-6aa2a4b1a3d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019ca091-8713-7ea1-959a-3d0f0cc144f8" xlink:to="loc_us-gaap_SalesRevenueNetMember_019ca091-8713-7360-bfee-6aa2a4b1a3d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_ReceivablesBenchmarkMember_019ca091-8713-7321-9712-500abe1c94cf" xlink:href="pwr-20260331.xsd#pwr_ReceivablesBenchmarkMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019ca091-8713-7ea1-959a-3d0f0cc144f8" xlink:to="loc_pwr_ReceivablesBenchmarkMember_019ca091-8713-7321-9712-500abe1c94cf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_019ca091-8713-76ea-ab77-f2598f937adc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019ca091-8713-733e-ba0e-c47e0699ae63" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_019ca091-8713-76ea-ab77-f2598f937adc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_CreditRiskGroupAxis_019ca091-8713-7764-911f-57953a3f8f12" xlink:href="pwr-20260331.xsd#pwr_CreditRiskGroupAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019ca091-8713-733e-ba0e-c47e0699ae63" xlink:to="loc_pwr_CreditRiskGroupAxis_019ca091-8713-7764-911f-57953a3f8f12" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_CreditRiskGroupDomain_019ca091-8713-7764-911f-57953a3f8f12_default" xlink:href="pwr-20260331.xsd#pwr_CreditRiskGroupDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_pwr_CreditRiskGroupAxis_019ca091-8713-7764-911f-57953a3f8f12" xlink:to="loc_pwr_CreditRiskGroupDomain_019ca091-8713-7764-911f-57953a3f8f12_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_CreditRiskGroupDomain_019ca091-8713-72ca-9c9c-81701209f6ad" xlink:href="pwr-20260331.xsd#pwr_CreditRiskGroupDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_pwr_CreditRiskGroupAxis_019ca091-8713-7764-911f-57953a3f8f12" xlink:to="loc_pwr_CreditRiskGroupDomain_019ca091-8713-72ca-9c9c-81701209f6ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SecondaryPoolMember_019ca091-8713-7715-a56b-9f775cac4cf9" xlink:href="pwr-20260331.xsd#pwr_SecondaryPoolMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pwr_CreditRiskGroupDomain_019ca091-8713-72ca-9c9c-81701209f6ad" xlink:to="loc_pwr_SecondaryPoolMember_019ca091-8713-7715-a56b-9f775cac4cf9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_019ca091-8713-77ae-b677-db62d981fe3f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019ca091-8713-733e-ba0e-c47e0699ae63" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_019ca091-8713-77ae-b677-db62d981fe3f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_019ca091-8713-77ae-b677-db62d981fe3f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_019ca091-8713-77ae-b677-db62d981fe3f" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_019ca091-8713-77ae-b677-db62d981fe3f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_019ca091-8713-7b14-b1ff-274aeff00d1e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_019ca091-8713-77ae-b677-db62d981fe3f" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_019ca091-8713-7b14-b1ff-274aeff00d1e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesMember_019ca091-8713-7e12-ad83-bc4ac6d27b87" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_019ca091-8713-7b14-b1ff-274aeff00d1e" xlink:to="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesMember_019ca091-8713-7e12-ad83-bc4ac6d27b87" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_019ca091-8713-7aea-b7d7-8e1327e3c6df" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019ca091-8713-733e-ba0e-c47e0699ae63" xlink:to="loc_srt_MajorCustomersAxis_019ca091-8713-7aea-b7d7-8e1327e3c6df" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019ca091-8713-7aea-b7d7-8e1327e3c6df_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_019ca091-8713-7aea-b7d7-8e1327e3c6df" xlink:to="loc_srt_NameOfMajorCustomerDomain_019ca091-8713-7aea-b7d7-8e1327e3c6df_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019ca091-8713-78b3-81d6-22b9711fb53a" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_019ca091-8713-7aea-b7d7-8e1327e3c6df" xlink:to="loc_srt_NameOfMajorCustomerDomain_019ca091-8713-78b3-81d6-22b9711fb53a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_CustomerMember_019ca091-8713-7eff-b0d3-3c3500afad88" xlink:href="pwr-20260331.xsd#pwr_CustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019ca091-8713-78b3-81d6-22b9711fb53a" xlink:to="loc_pwr_CustomerMember_019ca091-8713-7eff-b0d3-3c3500afad88" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_NumberOfServiceContractCategories_019ca091-8713-7c2e-b20c-2a3e96fe152f" xlink:href="pwr-20260331.xsd#pwr_NumberOfServiceContractCategories"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_pwr_NumberOfServiceContractCategories_019ca091-8713-7c2e-b20c-2a3e96fe152f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_RevenueFromContractWithCustomerPercentageOfRevenueRecognizedOverTime_019ca091-8713-7825-b208-1b8da004f290" xlink:href="pwr-20260331.xsd#pwr_RevenueFromContractWithCustomerPercentageOfRevenueRecognizedOverTime"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_pwr_RevenueFromContractWithCustomerPercentageOfRevenueRecognizedOverTime_019ca091-8713-7825-b208-1b8da004f290" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_019ca091-8713-779e-bd22-82a4731a71eb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_019ca091-8713-779e-bd22-82a4731a71eb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_019ca091-8713-73bc-b494-e95060bc7b6a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_019ca091-8713-73bc-b494-e95060bc7b6a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019ca091-8713-7ed3-ab50-316e2b62301b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019ca091-8713-7ed3-ab50-316e2b62301b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_ContractWithCustomerRevenueRecognizedRelatedToUnapprovedChangeOrdersAndClaims_019ca091-8713-7e45-b113-fd2617056f30" xlink:href="pwr-20260331.xsd#pwr_ContractWithCustomerRevenueRecognizedRelatedToUnapprovedChangeOrdersAndClaims"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_pwr_ContractWithCustomerRevenueRecognizedRelatedToUnapprovedChangeOrdersAndClaims_019ca091-8713-7e45-b113-fd2617056f30" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_ContractWithCustomerCumulativeCatchUpAdjustmentRevenueChangeInEstimatePercent_019ca091-8713-7d16-8822-bd8c8c951be6" xlink:href="pwr-20260331.xsd#pwr_ContractWithCustomerCumulativeCatchUpAdjustmentRevenueChangeInEstimatePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_pwr_ContractWithCustomerCumulativeCatchUpAdjustmentRevenueChangeInEstimatePercent_019ca091-8713-7d16-8822-bd8c8c951be6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_019ca091-8713-7496-8244-c0858fabd85f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_019ca091-8713-7496-8244-c0858fabd85f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_NumberOfRiskPools_019ca091-8713-71a8-a778-314c60eb9269" xlink:href="pwr-20260331.xsd#pwr_NumberOfRiskPools"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_pwr_NumberOfRiskPools_019ca091-8713-71a8-a778-314c60eb9269" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019ca091-8713-73d9-9ae0-97e9f2600fa8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019ca091-8713-73d9-9ae0-97e9f2600fa8" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_NumberOfCustomersRepresentingTenPercentOrMoreOfConsolidatedRevenues_019ca091-8713-7c00-a18b-c078036c8441" xlink:href="pwr-20260331.xsd#pwr_NumberOfCustomersRepresentingTenPercentOrMoreOfConsolidatedRevenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_pwr_NumberOfCustomersRepresentingTenPercentOrMoreOfConsolidatedRevenues_019ca091-8713-7c00-a18b-c078036c8441" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_NumberOfCustomersRepresentingTenPercentOrMoreOfNetReceivablePosition_019ca091-8713-7adf-b95a-1b488c51f1c2" xlink:href="pwr-20260331.xsd#pwr_NumberOfCustomersRepresentingTenPercentOrMoreOfNetReceivablePosition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_pwr_NumberOfCustomersRepresentingTenPercentOrMoreOfNetReceivablePosition_019ca091-8713-7adf-b95a-1b488c51f1c2" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerReceivableAfterAllowanceForCreditLossCurrent_019ca091-8713-77b1-99f5-77cc395079bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerReceivableAfterAllowanceForCreditLossCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_us-gaap_ContractWithCustomerReceivableAfterAllowanceForCreditLossCurrent_019ca091-8713-77b1-99f5-77cc395079bc" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerReceivableAfterAllowanceForCreditLossNoncurrent_019ca091-8713-7712-9bf8-9d0d8976d2a8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerReceivableAfterAllowanceForCreditLossNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_us-gaap_ContractWithCustomerReceivableAfterAllowanceForCreditLossNoncurrent_019ca091-8713-7712-9bf8-9d0d8976d2a8" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnbilledContractsReceivable_019ca091-8713-71a4-9d52-1b3f5efe7867" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnbilledContractsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_us-gaap_UnbilledContractsReceivable_019ca091-8713-71a4-9d52-1b3f5efe7867" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_ContractWithCustomerLiabilityDeferredRevenuesCurrent_019ca091-8713-7d27-81d4-a82f4ec00dfb" xlink:href="pwr-20260331.xsd#pwr_ContractWithCustomerLiabilityDeferredRevenuesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_pwr_ContractWithCustomerLiabilityDeferredRevenuesCurrent_019ca091-8713-7d27-81d4-a82f4ec00dfb" xlink:type="arc" order="15"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/RevenueRecognitionandRelatedBalanceSheetAccountsAdditionalInformationDetails_1" xlink:type="simple" xlink:href="pwr-20260331.xsd#RevenueRecognitionandRelatedBalanceSheetAccountsAdditionalInformationDetails_1"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/RevenueRecognitionandRelatedBalanceSheetAccountsAdditionalInformationDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019ca091-8713-733e-ba0e-c47e0699ae63" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019ca091-8713-733e-ba0e-c47e0699ae63" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019ca091-8713-7634-afd0-a5cacbf046d8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019ca091-8713-733e-ba0e-c47e0699ae63" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019ca091-8713-7634-afd0-a5cacbf046d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019ca091-8713-7634-afd0-a5cacbf046d8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019ca091-8713-7634-afd0-a5cacbf046d8" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019ca091-8713-7634-afd0-a5cacbf046d8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019ca091-8713-7238-a081-141144975fe2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019ca091-8713-7634-afd0-a5cacbf046d8" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019ca091-8713-7238-a081-141144975fe2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditConcentrationRiskMember_019ca091-8713-7de5-9832-c52838798034" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019ca091-8713-7238-a081-141144975fe2" xlink:to="loc_us-gaap_CreditConcentrationRiskMember_019ca091-8713-7de5-9832-c52838798034" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_019ca091-8713-7de4-a078-de12790bd163" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019ca091-8713-7238-a081-141144975fe2" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_019ca091-8713-7de4-a078-de12790bd163" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019ca091-8713-7c0b-839e-eff50f69783c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019ca091-8713-733e-ba0e-c47e0699ae63" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019ca091-8713-7c0b-839e-eff50f69783c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019ca091-8713-7c0b-839e-eff50f69783c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019ca091-8713-7c0b-839e-eff50f69783c" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019ca091-8713-7c0b-839e-eff50f69783c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019ca091-8713-7ea1-959a-3d0f0cc144f8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019ca091-8713-7c0b-839e-eff50f69783c" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019ca091-8713-7ea1-959a-3d0f0cc144f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_FinancialInstrumentsMember_019ca091-8713-718e-90ec-a166d72e9129" xlink:href="pwr-20260331.xsd#pwr_FinancialInstrumentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019ca091-8713-7ea1-959a-3d0f0cc144f8" xlink:to="loc_pwr_FinancialInstrumentsMember_019ca091-8713-718e-90ec-a166d72e9129" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_019ca091-8713-7360-bfee-6aa2a4b1a3d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019ca091-8713-7ea1-959a-3d0f0cc144f8" xlink:to="loc_us-gaap_SalesRevenueNetMember_019ca091-8713-7360-bfee-6aa2a4b1a3d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_ReceivablesBenchmarkMember_019ca091-8713-7321-9712-500abe1c94cf" xlink:href="pwr-20260331.xsd#pwr_ReceivablesBenchmarkMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019ca091-8713-7ea1-959a-3d0f0cc144f8" xlink:to="loc_pwr_ReceivablesBenchmarkMember_019ca091-8713-7321-9712-500abe1c94cf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_CreditRiskGroupAxis_019ca091-8713-7764-911f-57953a3f8f12" xlink:href="pwr-20260331.xsd#pwr_CreditRiskGroupAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019ca091-8713-733e-ba0e-c47e0699ae63" xlink:to="loc_pwr_CreditRiskGroupAxis_019ca091-8713-7764-911f-57953a3f8f12" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_CreditRiskGroupDomain_019ca091-8713-7764-911f-57953a3f8f12_default" xlink:href="pwr-20260331.xsd#pwr_CreditRiskGroupDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_pwr_CreditRiskGroupAxis_019ca091-8713-7764-911f-57953a3f8f12" xlink:to="loc_pwr_CreditRiskGroupDomain_019ca091-8713-7764-911f-57953a3f8f12_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_CreditRiskGroupDomain_019ca091-8713-72ca-9c9c-81701209f6ad" xlink:href="pwr-20260331.xsd#pwr_CreditRiskGroupDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_pwr_CreditRiskGroupAxis_019ca091-8713-7764-911f-57953a3f8f12" xlink:to="loc_pwr_CreditRiskGroupDomain_019ca091-8713-72ca-9c9c-81701209f6ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SecondaryPoolMember_019ca091-8713-7715-a56b-9f775cac4cf9" xlink:href="pwr-20260331.xsd#pwr_SecondaryPoolMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pwr_CreditRiskGroupDomain_019ca091-8713-72ca-9c9c-81701209f6ad" xlink:to="loc_pwr_SecondaryPoolMember_019ca091-8713-7715-a56b-9f775cac4cf9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_019ca091-8713-77ae-b677-db62d981fe3f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019ca091-8713-733e-ba0e-c47e0699ae63" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_019ca091-8713-77ae-b677-db62d981fe3f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_019ca091-8713-77ae-b677-db62d981fe3f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_019ca091-8713-77ae-b677-db62d981fe3f" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_019ca091-8713-77ae-b677-db62d981fe3f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_019ca091-8713-7b14-b1ff-274aeff00d1e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_019ca091-8713-77ae-b677-db62d981fe3f" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_019ca091-8713-7b14-b1ff-274aeff00d1e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesMember_019ca091-8713-7e12-ad83-bc4ac6d27b87" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_019ca091-8713-7b14-b1ff-274aeff00d1e" xlink:to="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesMember_019ca091-8713-7e12-ad83-bc4ac6d27b87" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_019ca091-8713-7aea-b7d7-8e1327e3c6df" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019ca091-8713-733e-ba0e-c47e0699ae63" xlink:to="loc_srt_MajorCustomersAxis_019ca091-8713-7aea-b7d7-8e1327e3c6df" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019ca091-8713-7aea-b7d7-8e1327e3c6df_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_019ca091-8713-7aea-b7d7-8e1327e3c6df" xlink:to="loc_srt_NameOfMajorCustomerDomain_019ca091-8713-7aea-b7d7-8e1327e3c6df_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019ca091-8713-78b3-81d6-22b9711fb53a" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_019ca091-8713-7aea-b7d7-8e1327e3c6df" xlink:to="loc_srt_NameOfMajorCustomerDomain_019ca091-8713-78b3-81d6-22b9711fb53a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_CustomerMember_019ca091-8713-7eff-b0d3-3c3500afad88" xlink:href="pwr-20260331.xsd#pwr_CustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019ca091-8713-78b3-81d6-22b9711fb53a" xlink:to="loc_pwr_CustomerMember_019ca091-8713-7eff-b0d3-3c3500afad88" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_NumberOfServiceContractCategories_019ca091-8713-7c2e-b20c-2a3e96fe152f" xlink:href="pwr-20260331.xsd#pwr_NumberOfServiceContractCategories"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_pwr_NumberOfServiceContractCategories_019ca091-8713-7c2e-b20c-2a3e96fe152f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_RevenueFromContractWithCustomerPercentageOfRevenueRecognizedOverTime_019ca091-8713-7825-b208-1b8da004f290" xlink:href="pwr-20260331.xsd#pwr_RevenueFromContractWithCustomerPercentageOfRevenueRecognizedOverTime"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_pwr_RevenueFromContractWithCustomerPercentageOfRevenueRecognizedOverTime_019ca091-8713-7825-b208-1b8da004f290" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_019ca091-8713-779e-bd22-82a4731a71eb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_019ca091-8713-779e-bd22-82a4731a71eb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_019ca091-8713-73bc-b494-e95060bc7b6a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_019ca091-8713-73bc-b494-e95060bc7b6a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019ca091-8713-7ed3-ab50-316e2b62301b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019ca091-8713-7ed3-ab50-316e2b62301b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_ContractWithCustomerRevenueRecognizedRelatedToUnapprovedChangeOrdersAndClaims_019ca091-8713-7e45-b113-fd2617056f30" xlink:href="pwr-20260331.xsd#pwr_ContractWithCustomerRevenueRecognizedRelatedToUnapprovedChangeOrdersAndClaims"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_pwr_ContractWithCustomerRevenueRecognizedRelatedToUnapprovedChangeOrdersAndClaims_019ca091-8713-7e45-b113-fd2617056f30" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_ContractWithCustomerCumulativeCatchUpAdjustmentRevenueChangeInEstimatePercent_019ca091-8713-7d16-8822-bd8c8c951be6" xlink:href="pwr-20260331.xsd#pwr_ContractWithCustomerCumulativeCatchUpAdjustmentRevenueChangeInEstimatePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_pwr_ContractWithCustomerCumulativeCatchUpAdjustmentRevenueChangeInEstimatePercent_019ca091-8713-7d16-8822-bd8c8c951be6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_019ca091-8713-7496-8244-c0858fabd85f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_019ca091-8713-7496-8244-c0858fabd85f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_NumberOfRiskPools_019ca091-8713-71a8-a778-314c60eb9269" xlink:href="pwr-20260331.xsd#pwr_NumberOfRiskPools"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_pwr_NumberOfRiskPools_019ca091-8713-71a8-a778-314c60eb9269" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019ca091-8713-73d9-9ae0-97e9f2600fa8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019ca091-8713-73d9-9ae0-97e9f2600fa8" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_NumberOfCustomersRepresentingTenPercentOrMoreOfConsolidatedRevenues_019ca091-8713-7c00-a18b-c078036c8441" xlink:href="pwr-20260331.xsd#pwr_NumberOfCustomersRepresentingTenPercentOrMoreOfConsolidatedRevenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_pwr_NumberOfCustomersRepresentingTenPercentOrMoreOfConsolidatedRevenues_019ca091-8713-7c00-a18b-c078036c8441" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_NumberOfCustomersRepresentingTenPercentOrMoreOfNetReceivablePosition_019ca091-8713-7adf-b95a-1b488c51f1c2" xlink:href="pwr-20260331.xsd#pwr_NumberOfCustomersRepresentingTenPercentOrMoreOfNetReceivablePosition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_pwr_NumberOfCustomersRepresentingTenPercentOrMoreOfNetReceivablePosition_019ca091-8713-7adf-b95a-1b488c51f1c2" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerReceivableAfterAllowanceForCreditLossCurrent_019ca091-8713-77b1-99f5-77cc395079bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerReceivableAfterAllowanceForCreditLossCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_us-gaap_ContractWithCustomerReceivableAfterAllowanceForCreditLossCurrent_019ca091-8713-77b1-99f5-77cc395079bc" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerReceivableAfterAllowanceForCreditLossNoncurrent_019ca091-8713-7712-9bf8-9d0d8976d2a8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerReceivableAfterAllowanceForCreditLossNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_us-gaap_ContractWithCustomerReceivableAfterAllowanceForCreditLossNoncurrent_019ca091-8713-7712-9bf8-9d0d8976d2a8" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnbilledContractsReceivable_019ca091-8713-71a4-9d52-1b3f5efe7867" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnbilledContractsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_us-gaap_UnbilledContractsReceivable_019ca091-8713-71a4-9d52-1b3f5efe7867" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_ContractWithCustomerLiabilityDeferredRevenuesCurrent_019ca091-8713-7d27-81d4-a82f4ec00dfb" xlink:href="pwr-20260331.xsd#pwr_ContractWithCustomerLiabilityDeferredRevenuesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ca091-8713-7c80-8748-33ef53befa50" xlink:to="loc_pwr_ContractWithCustomerLiabilityDeferredRevenuesCurrent_019ca091-8713-7d27-81d4-a82f4ec00dfb" xlink:type="arc" order="15"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/SegmentInformationSummarizedFinancialInformationDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#SegmentInformationSummarizedFinancialInformationDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/SegmentInformationSummarizedFinancialInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019ca091-8713-7516-9554-a01a4af47c94" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ca091-8713-7152-9b85-fa2148038b79" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ca091-8713-7516-9554-a01a4af47c94" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ca091-8713-7152-9b85-fa2148038b79" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019ca091-8713-7d35-9ca2-574ff73ae32e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ca091-8713-7152-9b85-fa2148038b79" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019ca091-8713-7d35-9ca2-574ff73ae32e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ca091-8713-7d35-9ca2-574ff73ae32e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ca091-8713-7d35-9ca2-574ff73ae32e" xlink:to="loc_us-gaap_SegmentDomain_019ca091-8713-7d35-9ca2-574ff73ae32e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ca091-8713-7563-a4e0-72760c650271" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ca091-8713-7d35-9ca2-574ff73ae32e" xlink:to="loc_us-gaap_SegmentDomain_019ca091-8713-7563-a4e0-72760c650271" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_ElectricMember_019ca091-8713-779e-9c64-08ff93f4357e" xlink:href="pwr-20260331.xsd#pwr_ElectricMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019ca091-8713-7563-a4e0-72760c650271" xlink:to="loc_pwr_ElectricMember_019ca091-8713-779e-9c64-08ff93f4357e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_UndergroundAndInfrastructureMember_019ca091-8713-7fbf-99e0-0518d59c5cce" xlink:href="pwr-20260331.xsd#pwr_UndergroundAndInfrastructureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019ca091-8713-7563-a4e0-72760c650271" xlink:to="loc_pwr_UndergroundAndInfrastructureMember_019ca091-8713-7fbf-99e0-0518d59c5cce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019ca091-8713-7480-bc28-fbf5fce3b3c5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ca091-8713-7152-9b85-fa2148038b79" xlink:to="loc_srt_ConsolidationItemsAxis_019ca091-8713-7480-bc28-fbf5fce3b3c5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019ca091-8713-7480-bc28-fbf5fce3b3c5_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019ca091-8713-7480-bc28-fbf5fce3b3c5" xlink:to="loc_srt_ConsolidationItemsDomain_019ca091-8713-7480-bc28-fbf5fce3b3c5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019ca091-8713-767d-9ee4-2367888398d3" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019ca091-8713-7480-bc28-fbf5fce3b3c5" xlink:to="loc_srt_ConsolidationItemsDomain_019ca091-8713-767d-9ee4-2367888398d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_019ca091-8713-71a4-b02a-62d19b0f72f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019ca091-8713-767d-9ee4-2367888398d3" xlink:to="loc_us-gaap_CorporateNonSegmentMember_019ca091-8713-71a4-b02a-62d19b0f72f7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019ca091-8713-7ef6-a37a-9e4d92fe88a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ca091-8713-7516-9554-a01a4af47c94" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019ca091-8713-7ef6-a37a-9e4d92fe88a7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SegmentOperatingExpensesExcludingDepreciation_019d87e9-50ab-7abe-b700-e8eb8618fb96" xlink:href="pwr-20260331.xsd#pwr_SegmentOperatingExpensesExcludingDepreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ca091-8713-7516-9554-a01a4af47c94" xlink:to="loc_pwr_SegmentOperatingExpensesExcludingDepreciation_019d87e9-50ab-7abe-b700-e8eb8618fb96" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SegmentDepreciation_019ca091-8713-7525-a918-4d77430065a2" xlink:href="pwr-20260331.xsd#pwr_SegmentDepreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ca091-8713-7516-9554-a01a4af47c94" xlink:to="loc_pwr_SegmentDepreciation_019ca091-8713-7525-a918-4d77430065a2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SegmentOperatingExpenses_019ca091-8713-783a-aec6-d9f7c6899d5b" xlink:href="pwr-20260331.xsd#pwr_SegmentOperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ca091-8713-7516-9554-a01a4af47c94" xlink:to="loc_pwr_SegmentOperatingExpenses_019ca091-8713-783a-aec6-d9f7c6899d5b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_IncomeLossFromEquityMethodInvestmentsIntegralUnconsolidatedAffiliates_019ca091-8713-70bd-92a5-ee46c761269f" xlink:href="pwr-20260331.xsd#pwr_IncomeLossFromEquityMethodInvestmentsIntegralUnconsolidatedAffiliates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ca091-8713-7516-9554-a01a4af47c94" xlink:to="loc_pwr_IncomeLossFromEquityMethodInvestmentsIntegralUnconsolidatedAffiliates_019ca091-8713-70bd-92a5-ee46c761269f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SegmentOperatingIncome_019ca091-8713-7a79-9e00-4f8ceb6e1414" xlink:href="pwr-20260331.xsd#pwr_SegmentOperatingIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ca091-8713-7516-9554-a01a4af47c94" xlink:to="loc_pwr_SegmentOperatingIncome_019ca091-8713-7a79-9e00-4f8ceb6e1414" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_OperatingIncomeLossMarginPercentage_019ca091-8713-7ed2-9111-18a5e57db42e" xlink:href="pwr-20260331.xsd#pwr_OperatingIncomeLossMarginPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ca091-8713-7516-9554-a01a4af47c94" xlink:to="loc_pwr_OperatingIncomeLossMarginPercentage_019ca091-8713-7ed2-9111-18a5e57db42e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_CorporateAndNonAllocatedCosts_019ca091-8713-7a36-b5d0-13aa16cc829e" xlink:href="pwr-20260331.xsd#pwr_CorporateAndNonAllocatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ca091-8713-7516-9554-a01a4af47c94" xlink:to="loc_pwr_CorporateAndNonAllocatedCosts_019ca091-8713-7a36-b5d0-13aa16cc829e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019ca091-8713-7f51-b242-0801a0fc2fb3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ca091-8713-7516-9554-a01a4af47c94" xlink:to="loc_us-gaap_OperatingIncomeLoss_019ca091-8713-7f51-b242-0801a0fc2fb3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentForAmortization_019ca091-8713-7208-a54e-74a979d0c3fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentForAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ca091-8713-7516-9554-a01a4af47c94" xlink:to="loc_us-gaap_AdjustmentForAmortization_019ca091-8713-7208-a54e-74a979d0c3fe" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_019ca091-8713-79ec-a4ce-71c735982150" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ca091-8713-7516-9554-a01a4af47c94" xlink:to="loc_us-gaap_ShareBasedCompensation_019ca091-8713-79ec-a4ce-71c735982150" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/AcquisitionsNarrativeDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#AcquisitionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/AcquisitionsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019ca091-8713-7af8-b395-711ac0f68bc0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019ca091-8713-7eb7-96c9-532a64d37b07" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ca091-8713-7af8-b395-711ac0f68bc0" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019ca091-8713-7eb7-96c9-532a64d37b07" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019ca091-8713-7d93-b6a3-0d5091720fb6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019ca091-8713-7eb7-96c9-532a64d37b07" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019ca091-8713-7d93-b6a3-0d5091720fb6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ca091-8713-7d93-b6a3-0d5091720fb6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019ca091-8713-7d93-b6a3-0d5091720fb6" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ca091-8713-7d93-b6a3-0d5091720fb6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ca091-8713-754a-9bc6-c0d396c2fc49" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019ca091-8713-7d93-b6a3-0d5091720fb6" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ca091-8713-754a-9bc6-c0d396c2fc49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_AcquisitionsMultiplePeriodsMember_019ca091-8713-7074-aa31-b8cff1a77c66" xlink:href="pwr-20260331.xsd#pwr_AcquisitionsMultiplePeriodsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ca091-8713-754a-9bc6-c0d396c2fc49" xlink:to="loc_pwr_AcquisitionsMultiplePeriodsMember_019ca091-8713-7074-aa31-b8cff1a77c66" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_DynamicSystemsLLCMember_019ca091-8713-75ad-89dd-48884c487abd" xlink:href="pwr-20260331.xsd#pwr_DynamicSystemsLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pwr_AcquisitionsMultiplePeriodsMember_019ca091-8713-7074-aa31-b8cff1a77c66" xlink:to="loc_pwr_DynamicSystemsLLCMember_019ca091-8713-75ad-89dd-48884c487abd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_019ca091-8713-751d-95e0-318a450340b4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pwr_AcquisitionsMultiplePeriodsMember_019ca091-8713-7074-aa31-b8cff1a77c66" xlink:to="loc_us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_019ca091-8713-751d-95e0-318a450340b4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_CivilSolutionsAcquisitionsMember_019ca091-8713-70f1-adc8-c56d7b6744b0" xlink:href="pwr-20260331.xsd#pwr_CivilSolutionsAcquisitionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pwr_AcquisitionsMultiplePeriodsMember_019ca091-8713-7074-aa31-b8cff1a77c66" xlink:to="loc_pwr_CivilSolutionsAcquisitionsMember_019ca091-8713-70f1-adc8-c56d7b6744b0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_Acquisitions2025ExcludingDynamicSystemsMember_019d07c2-256f-7aae-87ae-295d676f8c29" xlink:href="pwr-20260331.xsd#pwr_Acquisitions2025ExcludingDynamicSystemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ca091-8713-754a-9bc6-c0d396c2fc49" xlink:to="loc_pwr_Acquisitions2025ExcludingDynamicSystemsMember_019d07c2-256f-7aae-87ae-295d676f8c29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019ca091-8713-7486-813c-e2a9384b67f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019ca091-8713-7eb7-96c9-532a64d37b07" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019ca091-8713-7486-813c-e2a9384b67f7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ca091-8713-7486-813c-e2a9384b67f7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ca091-8713-7486-813c-e2a9384b67f7" xlink:to="loc_us-gaap_SegmentDomain_019ca091-8713-7486-813c-e2a9384b67f7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ca091-8713-78fe-908e-b42c861bd725" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ca091-8713-7486-813c-e2a9384b67f7" xlink:to="loc_us-gaap_SegmentDomain_019ca091-8713-78fe-908e-b42c861bd725" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_ElectricMember_019d87f2-cf6b-76b5-945d-360ee957af4c" xlink:href="pwr-20260331.xsd#pwr_ElectricMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019ca091-8713-78fe-908e-b42c861bd725" xlink:to="loc_pwr_ElectricMember_019d87f2-cf6b-76b5-945d-360ee957af4c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_019ca091-8713-7cbf-a612-f446c93aee3d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ca091-8713-7af8-b395-711ac0f68bc0" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_019ca091-8713-7cbf-a612-f446c93aee3d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019ca091-8713-7ac9-ad69-58e85dca07ce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ca091-8713-7af8-b395-711ac0f68bc0" xlink:to="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019ca091-8713-7ac9-ad69-58e85dca07ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_019ca091-8713-7630-8a2a-254d76b50579" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ca091-8713-7af8-b395-711ac0f68bc0" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_019ca091-8713-7630-8a2a-254d76b50579" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_019ca091-8713-7a5e-a70d-ff82aacb1c5c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ca091-8713-7af8-b395-711ac0f68bc0" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_019ca091-8713-7a5e-a70d-ff82aacb1c5c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_BusinessCombinationPeriodForPerformanceTargetsToBeAchieved_019ca091-8713-7d6a-8da1-daed6a18b542" xlink:href="pwr-20260331.xsd#pwr_BusinessCombinationPeriodForPerformanceTargetsToBeAchieved"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ca091-8713-7af8-b395-711ac0f68bc0" xlink:to="loc_pwr_BusinessCombinationPeriodForPerformanceTargetsToBeAchieved_019ca091-8713-7d6a-8da1-daed6a18b542" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_BusinessCombinationContingentConsiderationArrangementsPercentageOfConsiderationThatCanBePaidInStock_019ca091-8713-7fc4-8795-ff57601b69ef" xlink:href="pwr-20260331.xsd#pwr_BusinessCombinationContingentConsiderationArrangementsPercentageOfConsiderationThatCanBePaidInStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ca091-8713-7af8-b395-711ac0f68bc0" xlink:to="loc_pwr_BusinessCombinationContingentConsiderationArrangementsPercentageOfConsiderationThatCanBePaidInStock_019ca091-8713-7fc4-8795-ff57601b69ef" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfBusinessesAcquired_019ca091-8713-76c7-a2ce-21b7168f513c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NumberOfBusinessesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ca091-8713-7af8-b395-711ac0f68bc0" xlink:to="loc_us-gaap_NumberOfBusinessesAcquired_019ca091-8713-76c7-a2ce-21b7168f513c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_BusinessCombinationCashConsiderationTransferredOrToBeTransferred_019ca091-8713-7256-a4c4-ae4ca4ac2778" xlink:href="pwr-20260331.xsd#pwr_BusinessCombinationCashConsiderationTransferredOrToBeTransferred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ca091-8713-7af8-b395-711ac0f68bc0" xlink:to="loc_pwr_BusinessCombinationCashConsiderationTransferredOrToBeTransferred_019ca091-8713-7256-a4c4-ae4ca4ac2778" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_BusinessCombinationContingentConsiderationDiscretionaryAmountPayableInCommonStockPercentage_019d0811-14a7-7b4f-bcaf-6cd3d62e8e37" xlink:href="pwr-20260331.xsd#pwr_BusinessCombinationContingentConsiderationDiscretionaryAmountPayableInCommonStockPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ca091-8713-7af8-b395-711ac0f68bc0" xlink:to="loc_pwr_BusinessCombinationContingentConsiderationDiscretionaryAmountPayableInCommonStockPercentage_019d0811-14a7-7b4f-bcaf-6cd3d62e8e37" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetTangibleAssets_019ca091-8713-7374-b5df-1e558809ea00" xlink:href="pwr-20260331.xsd#pwr_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetTangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ca091-8713-7af8-b395-711ac0f68bc0" xlink:to="loc_pwr_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetTangibleAssets_019ca091-8713-7374-b5df-1e558809ea00" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinitelivedIntangibleAssetsAcquired1_019ca091-8713-7e3a-922f-fce27a4e0bc4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinitelivedIntangibleAssetsAcquired1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ca091-8713-7af8-b395-711ac0f68bc0" xlink:to="loc_us-gaap_FinitelivedIntangibleAssetsAcquired1_019ca091-8713-7e3a-922f-fce27a4e0bc4" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillAcquiredDuringPeriod_019ca091-8713-7ed8-b3cf-4df146264d8d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillAcquiredDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ca091-8713-7af8-b395-711ac0f68bc0" xlink:to="loc_us-gaap_GoodwillAcquiredDuringPeriod_019ca091-8713-7ed8-b3cf-4df146264d8d" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_019dd483-f9d7-7a51-9bce-4cbda59357dd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillPurchaseAccountingAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ca091-8713-7af8-b395-711ac0f68bc0" xlink:to="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_019dd483-f9d7-7a51-9bce-4cbda59357dd" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_PaymentForContingentConsiderationLiabilityOperatingAndFinancingActivities_019ca091-8713-76a3-bae8-0696d9b3bc24" xlink:href="pwr-20260331.xsd#pwr_PaymentForContingentConsiderationLiabilityOperatingAndFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ca091-8713-7af8-b395-711ac0f68bc0" xlink:to="loc_pwr_PaymentForContingentConsiderationLiabilityOperatingAndFinancingActivities_019ca091-8713-76a3-bae8-0696d9b3bc24" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_019ca091-8713-79ea-83dd-bfaaa730b58c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationAcquisitionRelatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ca091-8713-7af8-b395-711ac0f68bc0" xlink:to="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_019ca091-8713-79ea-83dd-bfaaa730b58c" xlink:type="arc" order="14"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/AcquisitionsAggregateFairValuesofOutstandingContingentConsiderationLiabilitiesDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#AcquisitionsAggregateFairValuesofOutstandingContingentConsiderationLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/AcquisitionsAggregateFairValuesofOutstandingContingentConsiderationLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_019ca091-8713-7321-b47e-70822560e915" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionContingentConsiderationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019ca091-8713-7ce3-8342-4d8c4944d538" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_019ca091-8713-7321-b47e-70822560e915" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019ca091-8713-7ce3-8342-4d8c4944d538" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_019ca091-8713-7ab6-9900-52c19d2f3906" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019ca091-8713-7ce3-8342-4d8c4944d538" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_019ca091-8713-7ab6-9900-52c19d2f3906" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_019ca091-8713-7ab6-9900-52c19d2f3906_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_019ca091-8713-7ab6-9900-52c19d2f3906" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_019ca091-8713-7ab6-9900-52c19d2f3906_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_019ca091-8713-718a-bf64-5c7d87accbd8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_019ca091-8713-7ab6-9900-52c19d2f3906" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_019ca091-8713-718a-bf64-5c7d87accbd8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesMember_019ca091-8713-7c7d-b20e-f88f5d57a703" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_019ca091-8713-718a-bf64-5c7d87accbd8" xlink:to="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesMember_019ca091-8713-7c7d-b20e-f88f5d57a703" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoncurrentLiabilitiesMember_019ca091-8713-78d6-9400-7a061b9933b2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNoncurrentLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_019ca091-8713-718a-bf64-5c7d87accbd8" xlink:to="loc_us-gaap_OtherNoncurrentLiabilitiesMember_019ca091-8713-78d6-9400-7a061b9933b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent_019ca091-8713-7463-9b7c-b349decb970c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_019ca091-8713-7321-b47e-70822560e915" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent_019ca091-8713-7463-9b7c-b349decb970c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent_019ca091-8713-7113-ba31-6d944db15299" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_019ca091-8713-7321-b47e-70822560e915" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent_019ca091-8713-7113-ba31-6d944db15299" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019ca091-8713-7e4f-b33f-88ffc15cf85d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_019ca091-8713-7321-b47e-70822560e915" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019ca091-8713-7e4f-b33f-88ffc15cf85d" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/AcquisitionsIncreaseFromAcquisitionsByYearDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#AcquisitionsIncreaseFromAcquisitionsByYearDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/AcquisitionsIncreaseFromAcquisitionsByYearDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019d081c-a8e8-7da6-b07b-a5cb6dcf6947" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019d081c-a8e7-71f8-a938-52c9720a2e4a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019d081c-a8e8-7da6-b07b-a5cb6dcf6947" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019d081c-a8e7-71f8-a938-52c9720a2e4a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019d081c-a8e7-7a5a-bfc8-e6613f0d79df" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019d081c-a8e7-71f8-a938-52c9720a2e4a" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019d081c-a8e7-7a5a-bfc8-e6613f0d79df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d081c-a8e7-7a5a-bfc8-e6613f0d79df_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019d081c-a8e7-7a5a-bfc8-e6613f0d79df" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d081c-a8e7-7a5a-bfc8-e6613f0d79df_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d081c-a8e7-738a-a496-da929da65ab7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019d081c-a8e7-7a5a-bfc8-e6613f0d79df" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d081c-a8e7-738a-a496-da929da65ab7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_019d081c-a8e7-75c4-b676-e771ca14e76a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d081c-a8e7-738a-a496-da929da65ab7" xlink:to="loc_us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_019d081c-a8e7-75c4-b676-e771ca14e76a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual_019d081c-a8e8-7da5-89ba-6c9b3875a725" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019d081c-a8e8-7da6-b07b-a5cb6dcf6947" xlink:to="loc_us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual_019d081c-a8e8-7da5-89ba-6c9b3875a725" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual_019d081c-a8e8-7de6-8ce0-d8c0b1be3125" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019d081c-a8e8-7da6-b07b-a5cb6dcf6947" xlink:to="loc_us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual_019d081c-a8e8-7de6-8ce0-d8c0b1be3125" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/InvestmentsinAffiliatesandOtherEntitiesEquityInvestmentsDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#InvestmentsinAffiliatesandOtherEntitiesEquityInvestmentsDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/InvestmentsinAffiliatesandOtherEntitiesEquityInvestmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ca091-8713-7747-acd8-302f55133be6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019ca091-8713-7845-94f5-b7c853b6019d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ca091-8713-7747-acd8-302f55133be6" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019ca091-8713-7845-94f5-b7c853b6019d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ca091-8713-782d-bcd2-9a534d34e3fb" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019ca091-8713-7845-94f5-b7c853b6019d" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ca091-8713-782d-bcd2-9a534d34e3fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019ca091-8713-782d-bcd2-9a534d34e3fb_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ca091-8713-782d-bcd2-9a534d34e3fb" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019ca091-8713-782d-bcd2-9a534d34e3fb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019ca091-8713-7f20-b754-58755b74f46e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ca091-8713-782d-bcd2-9a534d34e3fb" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019ca091-8713-7f20-b754-58755b74f46e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_IntegralAffiliatesMember_019ca091-8713-7057-b58e-0abedc58ec31" xlink:href="pwr-20260331.xsd#pwr_IntegralAffiliatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019ca091-8713-7f20-b754-58755b74f46e" xlink:to="loc_pwr_IntegralAffiliatesMember_019ca091-8713-7057-b58e-0abedc58ec31" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_NonIntegralUnconsolidatedAffiliatesMember_019ca091-8713-78d6-a11a-7ff891a1fbd4" xlink:href="pwr-20260331.xsd#pwr_NonIntegralUnconsolidatedAffiliatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019ca091-8713-7f20-b754-58755b74f46e" xlink:to="loc_pwr_NonIntegralUnconsolidatedAffiliatesMember_019ca091-8713-78d6-a11a-7ff891a1fbd4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestments_019ca091-8713-7770-9352-2bfa0ab09c3d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ca091-8713-7747-acd8-302f55133be6" xlink:to="loc_us-gaap_EquityMethodInvestments_019ca091-8713-7770-9352-2bfa0ab09c3d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount_019ca091-8713-75db-988c-7f7bd501e50d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ca091-8713-7747-acd8-302f55133be6" xlink:to="loc_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount_019ca091-8713-75db-988c-7f7bd501e50d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermInvestments_019ca091-8713-7bcd-87f9-630c663aa3bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ca091-8713-7747-acd8-302f55133be6" xlink:to="loc_us-gaap_LongTermInvestments_019ca091-8713-7bcd-87f9-630c663aa3bc" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/InvestmentsinAffiliatesandOtherEntitiesNarrativeDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#InvestmentsinAffiliatesandOtherEntitiesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/InvestmentsinAffiliatesandOtherEntitiesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ca091-8713-764a-8017-9c50a5d42646" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019ca091-8713-72ee-9f90-8d016b55fbbf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ca091-8713-764a-8017-9c50a5d42646" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019ca091-8713-72ee-9f90-8d016b55fbbf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ca091-8713-7db8-a8a3-45f25622d35c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019ca091-8713-72ee-9f90-8d016b55fbbf" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ca091-8713-7db8-a8a3-45f25622d35c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019ca091-8713-7db8-a8a3-45f25622d35c_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ca091-8713-7db8-a8a3-45f25622d35c" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019ca091-8713-7db8-a8a3-45f25622d35c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019ca091-8713-736d-951e-48aed1986d32" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ca091-8713-7db8-a8a3-45f25622d35c" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019ca091-8713-736d-951e-48aed1986d32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_IntegralAffiliatesMember_019ca091-8713-7c14-a137-d3e6c3ea341c" xlink:href="pwr-20260331.xsd#pwr_IntegralAffiliatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019ca091-8713-736d-951e-48aed1986d32" xlink:to="loc_pwr_IntegralAffiliatesMember_019ca091-8713-7c14-a137-d3e6c3ea341c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_NonIntegralUnconsolidatedAffiliatesMember_019ca091-8713-74ea-9226-bb4fa46e1140" xlink:href="pwr-20260331.xsd#pwr_NonIntegralUnconsolidatedAffiliatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019ca091-8713-736d-951e-48aed1986d32" xlink:to="loc_pwr_NonIntegralUnconsolidatedAffiliatesMember_019ca091-8713-74ea-9226-bb4fa46e1140" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_IntegralUnconsolidatedAffiliatesMember_019ca091-8713-7912-9682-796488d6e1de" xlink:href="pwr-20260331.xsd#pwr_IntegralUnconsolidatedAffiliatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019ca091-8713-736d-951e-48aed1986d32" xlink:to="loc_pwr_IntegralUnconsolidatedAffiliatesMember_019ca091-8713-7912-9682-796488d6e1de" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_IntegralAndNonIntegralUnconsolidatedAffiliatesMember_019ca091-8713-7390-8cd5-d7eefed2b818" xlink:href="pwr-20260331.xsd#pwr_IntegralAndNonIntegralUnconsolidatedAffiliatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019ca091-8713-736d-951e-48aed1986d32" xlink:to="loc_pwr_IntegralAndNonIntegralUnconsolidatedAffiliatesMember_019ca091-8713-7390-8cd5-d7eefed2b818" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ca091-8713-79cb-a9a0-aff7cbb0ac70" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019ca091-8713-72ee-9f90-8d016b55fbbf" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ca091-8713-79cb-a9a0-aff7cbb0ac70" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019ca091-8713-79cb-a9a0-aff7cbb0ac70_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ca091-8713-79cb-a9a0-aff7cbb0ac70" xlink:to="loc_us-gaap_RelatedPartyDomain_019ca091-8713-79cb-a9a0-aff7cbb0ac70_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019ca091-8713-7155-9cd5-6c734d2ca463" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ca091-8713-79cb-a9a0-aff7cbb0ac70" xlink:to="loc_us-gaap_RelatedPartyDomain_019ca091-8713-7155-9cd5-6c734d2ca463" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019ca091-8713-72f7-bc4b-faf0632e3702" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019ca091-8713-7155-9cd5-6c734d2ca463" xlink:to="loc_us-gaap_RelatedPartyMember_019ca091-8713-72f7-bc4b-faf0632e3702" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_019ca091-8713-7c68-8c86-45dfb6979318" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ca091-8713-764a-8017-9c50a5d42646" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_019ca091-8713-7c68-8c86-45dfb6979318" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_019ca091-8713-7bb4-b756-b922871c427a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ca091-8713-764a-8017-9c50a5d42646" xlink:to="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_019ca091-8713-7bb4-b756-b922871c427a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019ca091-8713-751a-934a-e0362f8ff612" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ca091-8713-764a-8017-9c50a5d42646" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019ca091-8713-751a-934a-e0362f8ff612" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_019ca091-8713-76c8-aae3-de32eab536b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ca091-8713-764a-8017-9c50a5d42646" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_019ca091-8713-76c8-aae3-de32eab536b9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_IncomeLossFromEquityMethodInvestmentsIntegralUnconsolidatedAffiliates_019ca091-8713-7961-8479-f39662f7dd5b" xlink:href="pwr-20260331.xsd#pwr_IncomeLossFromEquityMethodInvestmentsIntegralUnconsolidatedAffiliates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ca091-8713-764a-8017-9c50a5d42646" xlink:to="loc_pwr_IncomeLossFromEquityMethodInvestmentsIntegralUnconsolidatedAffiliates_019ca091-8713-7961-8479-f39662f7dd5b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_IncomeLossFromEquityMethodInvestmentsNonIntegralUnconsolidatedAffiliates_019ca091-8713-791d-9e67-a1386bca0ea8" xlink:href="pwr-20260331.xsd#pwr_IncomeLossFromEquityMethodInvestmentsNonIntegralUnconsolidatedAffiliates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ca091-8713-764a-8017-9c50a5d42646" xlink:to="loc_pwr_IncomeLossFromEquityMethodInvestmentsNonIntegralUnconsolidatedAffiliates_019ca091-8713-791d-9e67-a1386bca0ea8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsUndistributedEarningsFromEquityMethodInvestees_019ca091-8713-711c-a691-92f2945ba437" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsUndistributedEarningsFromEquityMethodInvestees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ca091-8713-764a-8017-9c50a5d42646" xlink:to="loc_us-gaap_RetainedEarningsUndistributedEarningsFromEquityMethodInvestees_019ca091-8713-711c-a691-92f2945ba437" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquity_019ca091-8713-7b92-a799-34d4cf363c03" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ca091-8713-764a-8017-9c50a5d42646" xlink:to="loc_us-gaap_EquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquity_019ca091-8713-7b92-a799-34d4cf363c03" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_AmortizationOfEquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquity_019db6f7-6992-7e3e-bf49-ea069adba78a" xlink:href="pwr-20260331.xsd#pwr_AmortizationOfEquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ca091-8713-764a-8017-9c50a5d42646" xlink:to="loc_pwr_AmortizationOfEquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquity_019db6f7-6992-7e3e-bf49-ea069adba78a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueImpairmentLossCumulativeAmount_019daccd-cfb2-7b3c-bf67-0f3df89e251a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueImpairmentLossCumulativeAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019ca091-8713-764a-8017-9c50a5d42646" xlink:to="loc_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueImpairmentLossCumulativeAmount_019daccd-cfb2-7b3c-bf67-0f3df89e251a" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/DebtObligationsLongtermDebtObligationsDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#DebtObligationsLongtermDebtObligationsDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/DebtObligationsLongtermDebtObligationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-7bdd-868b-403e52e6c82d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019ca091-8713-7adf-bcee-ce0d0202fb69" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-7bdd-868b-403e52e6c82d" xlink:to="loc_us-gaap_DebtInstrumentTable_019ca091-8713-7adf-bcee-ce0d0202fb69" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019ca091-8713-7181-b187-53bc845e88a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ca091-8713-7adf-bcee-ce0d0202fb69" xlink:to="loc_us-gaap_DebtInstrumentAxis_019ca091-8713-7181-b187-53bc845e88a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ca091-8713-7181-b187-53bc845e88a7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ca091-8713-7181-b187-53bc845e88a7" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ca091-8713-7181-b187-53bc845e88a7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ca091-8713-71a2-b358-2dc91ab61468" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ca091-8713-7181-b187-53bc845e88a7" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ca091-8713-71a2-b358-2dc91ab61468" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SeniorNotesDueAugust2027Member_019ca091-8713-71b3-a649-13f04e4baa2f" xlink:href="pwr-20260331.xsd#pwr_SeniorNotesDueAugust2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-8713-71a2-b358-2dc91ab61468" xlink:to="loc_pwr_SeniorNotesDueAugust2027Member_019ca091-8713-71b3-a649-13f04e4baa2f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SeniorNotesDueAugust2028Member_019ca091-8713-7d52-be3f-b1c49a74c93c" xlink:href="pwr-20260331.xsd#pwr_SeniorNotesDueAugust2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-8713-71a2-b358-2dc91ab61468" xlink:to="loc_pwr_SeniorNotesDueAugust2028Member_019ca091-8713-7d52-be3f-b1c49a74c93c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SeniorNotesDueOctober2030Member_019ca091-8713-7ac9-8c27-4a73a0953b6e" xlink:href="pwr-20260331.xsd#pwr_SeniorNotesDueOctober2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-8713-71a2-b358-2dc91ab61468" xlink:to="loc_pwr_SeniorNotesDueOctober2030Member_019ca091-8713-7ac9-8c27-4a73a0953b6e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SeniorNotesDueJanuary2031Member_019ca091-8713-7199-a34b-7f11043bb92e" xlink:href="pwr-20260331.xsd#pwr_SeniorNotesDueJanuary2031Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-8713-71a2-b358-2dc91ab61468" xlink:to="loc_pwr_SeniorNotesDueJanuary2031Member_019ca091-8713-7199-a34b-7f11043bb92e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SeniorNotesDueJanuary2032Member_019ca091-8713-7286-af35-7649e6639046" xlink:href="pwr-20260331.xsd#pwr_SeniorNotesDueJanuary2032Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-8713-71a2-b358-2dc91ab61468" xlink:to="loc_pwr_SeniorNotesDueJanuary2032Member_019ca091-8713-7286-af35-7649e6639046" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SeniorNotesDueAugust2034Member_019ca091-8713-7746-b666-52b4522f7f43" xlink:href="pwr-20260331.xsd#pwr_SeniorNotesDueAugust2034Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-8713-71a2-b358-2dc91ab61468" xlink:to="loc_pwr_SeniorNotesDueAugust2034Member_019ca091-8713-7746-b666-52b4522f7f43" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SeniorNotesDueAugust2035Member_019ca091-8713-7187-a668-fdfe62102759" xlink:href="pwr-20260331.xsd#pwr_SeniorNotesDueAugust2035Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-8713-71a2-b358-2dc91ab61468" xlink:to="loc_pwr_SeniorNotesDueAugust2035Member_019ca091-8713-7187-a668-fdfe62102759" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SeniorNotesDueOctober2041Member_019ca091-8713-7193-b43d-a752959619b1" xlink:href="pwr-20260331.xsd#pwr_SeniorNotesDueOctober2041Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-8713-71a2-b358-2dc91ab61468" xlink:to="loc_pwr_SeniorNotesDueOctober2041Member_019ca091-8713-7193-b43d-a752959619b1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_CommercialPaperProgramMember_019d081f-07d1-77ca-8c8c-954900d2ec09" xlink:href="pwr-20260331.xsd#pwr_CommercialPaperProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-8713-71a2-b358-2dc91ab61468" xlink:to="loc_pwr_CommercialPaperProgramMember_019d081f-07d1-77ca-8c8c-954900d2ec09" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019ca091-87c5-7ed0-a2d5-ea58d171eeb2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ca091-8713-7adf-bcee-ce0d0202fb69" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019ca091-87c5-7ed0-a2d5-ea58d171eeb2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-7ed0-a2d5-ea58d171eeb2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ca091-87c5-7ed0-a2d5-ea58d171eeb2" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-7ed0-a2d5-ea58d171eeb2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-79cd-ad8f-97e00b835f3c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ca091-87c5-7ed0-a2d5-ea58d171eeb2" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-79cd-ad8f-97e00b835f3c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_019ca091-87c5-75ca-ba86-f4b086bb51b4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-79cd-ad8f-97e00b835f3c" xlink:to="loc_us-gaap_SeniorNotesMember_019ca091-87c5-75ca-ba86-f4b086bb51b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_019ca091-87c5-716e-8dd9-21002e01cb50" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-79cd-ad8f-97e00b835f3c" xlink:to="loc_us-gaap_CommercialPaperMember_019ca091-87c5-716e-8dd9-21002e01cb50" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019ca091-87c5-79a1-bd09-f3884edaab04" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-7bdd-868b-403e52e6c82d" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019ca091-87c5-79a1-bd09-f3884edaab04" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019ca091-87c5-715f-8270-9f0f1b0ee21b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-7bdd-868b-403e52e6c82d" xlink:to="loc_us-gaap_LongTermDebt_019ca091-87c5-715f-8270-9f0f1b0ee21b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019ca091-87c5-7ab2-8ba9-8eb9bd6f196d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-7bdd-868b-403e52e6c82d" xlink:to="loc_us-gaap_LineOfCredit_019ca091-87c5-7ab2-8ba9-8eb9bd6f196d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaper_019d081f-07d1-7a0d-8088-faef6e3ad322" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialPaper"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-7bdd-868b-403e52e6c82d" xlink:to="loc_us-gaap_CommercialPaper_019d081f-07d1-7a0d-8088-faef6e3ad322" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_LeaseFinancingTransactionLiability_019ca091-87c5-79d3-80d9-a520971e88cb" xlink:href="pwr-20260331.xsd#pwr_LeaseFinancingTransactionLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-7bdd-868b-403e52e6c82d" xlink:to="loc_pwr_LeaseFinancingTransactionLiability_019ca091-87c5-79d3-80d9-a520971e88cb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLongTermDebt_019ca091-87c5-79b9-b9c8-a48a29370634" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-7bdd-868b-403e52e6c82d" xlink:to="loc_us-gaap_OtherLongTermDebt_019ca091-87c5-79b9-b9c8-a48a29370634" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiability_019ca091-87c5-7fd7-a37a-6659b49065b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinanceLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-7bdd-868b-403e52e6c82d" xlink:to="loc_us-gaap_FinanceLeaseLiability_019ca091-87c5-7fd7-a37a-6659b49065b6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_019ca091-87c5-7b7d-a8cc-f24f5d5bca0b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-7bdd-868b-403e52e6c82d" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_019ca091-87c5-7b7d-a8cc-f24f5d5bca0b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtAndCapitalLeaseObligationsIncludingCurrentMaturities_019ca091-87c5-740e-8963-9fb062b5d2fc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtAndCapitalLeaseObligationsIncludingCurrentMaturities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-7bdd-868b-403e52e6c82d" xlink:to="loc_us-gaap_LongTermDebtAndCapitalLeaseObligationsIncludingCurrentMaturities_019ca091-87c5-740e-8963-9fb062b5d2fc" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtAndCapitalLeaseObligationsCurrent_019ca091-87c5-7d17-a81c-9dff9f21c984" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtAndCapitalLeaseObligationsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-7bdd-868b-403e52e6c82d" xlink:to="loc_us-gaap_LongTermDebtAndCapitalLeaseObligationsCurrent_019ca091-87c5-7d17-a81c-9dff9f21c984" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_019ca091-87c5-70b3-b52f-2c5870a57897" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtAndCapitalLeaseObligations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-7bdd-868b-403e52e6c82d" xlink:to="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_019ca091-87c5-70b3-b52f-2c5870a57897" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/DebtObligationsSeniorNotesNarrativeDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#DebtObligationsSeniorNotesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/DebtObligationsSeniorNotesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-76cf-bad8-d2ac0eeec592" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019ca091-87c5-73d8-9a68-3edcfeb52bfb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-76cf-bad8-d2ac0eeec592" xlink:to="loc_us-gaap_DebtInstrumentTable_019ca091-87c5-73d8-9a68-3edcfeb52bfb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019ca091-87c5-7937-9635-ef48f5367298" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ca091-87c5-73d8-9a68-3edcfeb52bfb" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019ca091-87c5-7937-9635-ef48f5367298" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-7937-9635-ef48f5367298_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ca091-87c5-7937-9635-ef48f5367298" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-7937-9635-ef48f5367298_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-7f3e-90b3-6ff0bb9923ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ca091-87c5-7937-9635-ef48f5367298" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-7f3e-90b3-6ff0bb9923ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_019ca091-87c5-70dc-90fb-311118294181" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-7f3e-90b3-6ff0bb9923ca" xlink:to="loc_us-gaap_SeniorNotesMember_019ca091-87c5-70dc-90fb-311118294181" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019ca091-87c5-77eb-8d79-9972822e8e26" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-76cf-bad8-d2ac0eeec592" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019ca091-87c5-77eb-8d79-9972822e8e26" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_019ca091-87c5-7545-b2b3-543a65b46946" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-76cf-bad8-d2ac0eeec592" xlink:to="loc_us-gaap_LongTermDebtFairValue_019ca091-87c5-7545-b2b3-543a65b46946" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019ca091-87c5-7697-9ac8-ae9227157156" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-76cf-bad8-d2ac0eeec592" xlink:to="loc_us-gaap_LongTermDebt_019ca091-87c5-7697-9ac8-ae9227157156" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_019ca091-87c5-7eb5-9251-500396eefc1f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-76cf-bad8-d2ac0eeec592" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_019ca091-87c5-7eb5-9251-500396eefc1f" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/DebtObligationsSeniorNotesDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#DebtObligationsSeniorNotesDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/DebtObligationsSeniorNotesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-708f-aad4-c3bb7e76b035" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019ca091-87c5-7221-a191-4dcaa0245db3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-708f-aad4-c3bb7e76b035" xlink:to="loc_us-gaap_DebtInstrumentTable_019ca091-87c5-7221-a191-4dcaa0245db3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019ca091-87c5-72df-8a7b-2cc85d243a03" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ca091-87c5-7221-a191-4dcaa0245db3" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019ca091-87c5-72df-8a7b-2cc85d243a03" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-72df-8a7b-2cc85d243a03_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ca091-87c5-72df-8a7b-2cc85d243a03" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-72df-8a7b-2cc85d243a03_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-77ad-b04a-69ffe5f00373" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ca091-87c5-72df-8a7b-2cc85d243a03" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-77ad-b04a-69ffe5f00373" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_019ca091-87c5-7a16-b1fe-1ef4fcbd8a6d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-77ad-b04a-69ffe5f00373" xlink:to="loc_us-gaap_SeniorNotesMember_019ca091-87c5-7a16-b1fe-1ef4fcbd8a6d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019ca091-87c5-7ccc-a941-19d6e9f8d154" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ca091-87c5-7221-a191-4dcaa0245db3" xlink:to="loc_us-gaap_DebtInstrumentAxis_019ca091-87c5-7ccc-a941-19d6e9f8d154" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7ccc-a941-19d6e9f8d154_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ca091-87c5-7ccc-a941-19d6e9f8d154" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7ccc-a941-19d6e9f8d154_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7e6c-b80c-b83affd12d6a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ca091-87c5-7ccc-a941-19d6e9f8d154" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7e6c-b80c-b83affd12d6a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SeniorNotesDueAugust2027Member_019ca091-87c5-736f-8785-aa8e17a7d1b9" xlink:href="pwr-20260331.xsd#pwr_SeniorNotesDueAugust2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7e6c-b80c-b83affd12d6a" xlink:to="loc_pwr_SeniorNotesDueAugust2027Member_019ca091-87c5-736f-8785-aa8e17a7d1b9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SeniorNotesDueAugust2028Member_019ca091-87c5-77cf-b758-84bbe3861a2e" xlink:href="pwr-20260331.xsd#pwr_SeniorNotesDueAugust2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7e6c-b80c-b83affd12d6a" xlink:to="loc_pwr_SeniorNotesDueAugust2028Member_019ca091-87c5-77cf-b758-84bbe3861a2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SeniorNotesDueOctober2030Member_019ca091-87c5-7c62-b511-f9ea443c09e7" xlink:href="pwr-20260331.xsd#pwr_SeniorNotesDueOctober2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7e6c-b80c-b83affd12d6a" xlink:to="loc_pwr_SeniorNotesDueOctober2030Member_019ca091-87c5-7c62-b511-f9ea443c09e7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SeniorNotesDueJanuary2031Member_019ca091-87c5-75fc-b948-1690c7db7c49" xlink:href="pwr-20260331.xsd#pwr_SeniorNotesDueJanuary2031Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7e6c-b80c-b83affd12d6a" xlink:to="loc_pwr_SeniorNotesDueJanuary2031Member_019ca091-87c5-75fc-b948-1690c7db7c49" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SeniorNotesDueJanuary2032Member_019ca091-87c5-7ccc-be72-ab0aa2a0e2df" xlink:href="pwr-20260331.xsd#pwr_SeniorNotesDueJanuary2032Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7e6c-b80c-b83affd12d6a" xlink:to="loc_pwr_SeniorNotesDueJanuary2032Member_019ca091-87c5-7ccc-be72-ab0aa2a0e2df" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SeniorNotesDueAugust2034Member_019ca091-87c5-71bc-a7a1-e029495fc25d" xlink:href="pwr-20260331.xsd#pwr_SeniorNotesDueAugust2034Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7e6c-b80c-b83affd12d6a" xlink:to="loc_pwr_SeniorNotesDueAugust2034Member_019ca091-87c5-71bc-a7a1-e029495fc25d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SeniorNotesDueAugust2035Member_019ca091-87c5-7e6e-8a15-0f7d4a1e588e" xlink:href="pwr-20260331.xsd#pwr_SeniorNotesDueAugust2035Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7e6c-b80c-b83affd12d6a" xlink:to="loc_pwr_SeniorNotesDueAugust2035Member_019ca091-87c5-7e6e-8a15-0f7d4a1e588e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SeniorNotesDueOctober2041Member_019ca091-87c5-75a2-9d41-e040bde27cc5" xlink:href="pwr-20260331.xsd#pwr_SeniorNotesDueOctober2041Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7e6c-b80c-b83affd12d6a" xlink:to="loc_pwr_SeniorNotesDueOctober2041Member_019ca091-87c5-75a2-9d41-e040bde27cc5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019ca091-87c5-7f8d-87e0-36c31698fbcd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-708f-aad4-c3bb7e76b035" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019ca091-87c5-7f8d-87e0-36c31698fbcd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentPeriodicPaymentInterest_019ca091-87c5-76c0-ab4c-239060115693" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentPeriodicPaymentInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-708f-aad4-c3bb7e76b035" xlink:to="loc_us-gaap_DebtInstrumentPeriodicPaymentInterest_019ca091-87c5-76c0-ab4c-239060115693" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/DebtObligationsSeniorCreditFacilityNarrativeDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#DebtObligationsSeniorCreditFacilityNarrativeDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/DebtObligationsSeniorCreditFacilityNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_019ca091-87c5-7824-beb3-333aa1f29dd7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_019ca091-87c5-720c-bd5a-12cc687610b5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ca091-87c5-7824-beb3-333aa1f29dd7" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_019ca091-87c5-720c-bd5a-12cc687610b5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019ca091-87c5-7646-9590-3ac65a6e0d7e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019ca091-87c5-720c-bd5a-12cc687610b5" xlink:to="loc_us-gaap_CreditFacilityAxis_019ca091-87c5-7646-9590-3ac65a6e0d7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019ca091-87c5-7646-9590-3ac65a6e0d7e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019ca091-87c5-7646-9590-3ac65a6e0d7e" xlink:to="loc_us-gaap_CreditFacilityDomain_019ca091-87c5-7646-9590-3ac65a6e0d7e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019ca091-87c5-7c2f-93d8-49c5107639f5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019ca091-87c5-7646-9590-3ac65a6e0d7e" xlink:to="loc_us-gaap_CreditFacilityDomain_019ca091-87c5-7c2f-93d8-49c5107639f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_TermLoanMember_019ca091-87c5-709d-a135-4d381e98937c" xlink:href="pwr-20260331.xsd#pwr_TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019ca091-87c5-7c2f-93d8-49c5107639f5" xlink:to="loc_pwr_TermLoanMember_019ca091-87c5-709d-a135-4d381e98937c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019ca091-87c5-7669-bbc9-03ed7d7fd58c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019ca091-87c5-7c2f-93d8-49c5107639f5" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019ca091-87c5-7669-bbc9-03ed7d7fd58c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_019ca091-87c5-79d5-9dcf-6d2942053d4c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019ca091-87c5-7c2f-93d8-49c5107639f5" xlink:to="loc_us-gaap_LetterOfCreditMember_019ca091-87c5-79d5-9dcf-6d2942053d4c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019ca091-87c5-74d0-bb6b-504a13a1bf6e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019ca091-87c5-720c-bd5a-12cc687610b5" xlink:to="loc_us-gaap_DebtInstrumentAxis_019ca091-87c5-74d0-bb6b-504a13a1bf6e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-74d0-bb6b-504a13a1bf6e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ca091-87c5-74d0-bb6b-504a13a1bf6e" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-74d0-bb6b-504a13a1bf6e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7834-ab1c-96f88487c253" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ca091-87c5-74d0-bb6b-504a13a1bf6e" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7834-ab1c-96f88487c253" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SeniorCreditFacilityMember_019ca091-87c5-7eee-b4c3-eedaed16da92" xlink:href="pwr-20260331.xsd#pwr_SeniorCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7834-ab1c-96f88487c253" xlink:to="loc_pwr_SeniorCreditFacilityMember_019ca091-87c5-7eee-b4c3-eedaed16da92" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019ca091-87c5-73a2-b7a8-bd65f92ebe62" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019ca091-87c5-720c-bd5a-12cc687610b5" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019ca091-87c5-73a2-b7a8-bd65f92ebe62" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-73a2-b7a8-bd65f92ebe62_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ca091-87c5-73a2-b7a8-bd65f92ebe62" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-73a2-b7a8-bd65f92ebe62_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-7123-97b7-713249e3415e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ca091-87c5-73a2-b7a8-bd65f92ebe62" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-7123-97b7-713249e3415e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019ca091-87c5-774b-b916-40e7089cc15c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-7123-97b7-713249e3415e" xlink:to="loc_us-gaap_LineOfCreditMember_019ca091-87c5-774b-b916-40e7089cc15c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019ca091-87c5-7dcd-a1d5-95d3084aca1b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ca091-87c5-7824-beb3-333aa1f29dd7" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019ca091-87c5-7dcd-a1d5-95d3084aca1b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019ca091-87c5-7854-8fa7-a103353a78e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ca091-87c5-7824-beb3-333aa1f29dd7" xlink:to="loc_us-gaap_LineOfCredit_019ca091-87c5-7854-8fa7-a103353a78e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_019ca091-87c5-73a5-b852-f5f3c7763a5c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ca091-87c5-7824-beb3-333aa1f29dd7" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_019ca091-87c5-73a5-b852-f5f3c7763a5c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_019ca091-87c5-7fc0-b3ea-388d09a71970" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ca091-87c5-7824-beb3-333aa1f29dd7" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_019ca091-87c5-7fc0-b3ea-388d09a71970" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/DebtObligationsSeniorCreditFacilityandCommercialPaperProgramScheduleDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#DebtObligationsSeniorCreditFacilityandCommercialPaperProgramScheduleDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/DebtObligationsSeniorCreditFacilityandCommercialPaperProgramScheduleDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_019ca091-87c5-76f9-b33f-ddca767f82b2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_019ca091-87c5-70b2-951e-7891d0107352" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ca091-87c5-76f9-b33f-ddca767f82b2" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_019ca091-87c5-70b2-951e-7891d0107352" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019ca091-87c5-71e2-b178-126810c838bb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019ca091-87c5-70b2-951e-7891d0107352" xlink:to="loc_us-gaap_DebtInstrumentAxis_019ca091-87c5-71e2-b178-126810c838bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-71e2-b178-126810c838bb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ca091-87c5-71e2-b178-126810c838bb" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-71e2-b178-126810c838bb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7ed2-8527-f9107d8b7c99" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ca091-87c5-71e2-b178-126810c838bb" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7ed2-8527-f9107d8b7c99" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SeniorCreditFacilityMember_019ca091-87c5-7905-a1ce-4c2651f6d412" xlink:href="pwr-20260331.xsd#pwr_SeniorCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7ed2-8527-f9107d8b7c99" xlink:to="loc_pwr_SeniorCreditFacilityMember_019ca091-87c5-7905-a1ce-4c2651f6d412" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_CommercialPaperProgramMember_019ca091-87c5-744f-bca3-26c6eb0b70f5" xlink:href="pwr-20260331.xsd#pwr_CommercialPaperProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7ed2-8527-f9107d8b7c99" xlink:to="loc_pwr_CommercialPaperProgramMember_019ca091-87c5-744f-bca3-26c6eb0b70f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019ca091-87c5-7843-befa-7d29a8c398ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019ca091-87c5-70b2-951e-7891d0107352" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019ca091-87c5-7843-befa-7d29a8c398ea" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-7843-befa-7d29a8c398ea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ca091-87c5-7843-befa-7d29a8c398ea" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-7843-befa-7d29a8c398ea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-718c-b38a-92721ba99182" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ca091-87c5-7843-befa-7d29a8c398ea" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-718c-b38a-92721ba99182" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019ca091-87c5-7780-93bb-fe6482c6e27a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-718c-b38a-92721ba99182" xlink:to="loc_us-gaap_LineOfCreditMember_019ca091-87c5-7780-93bb-fe6482c6e27a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_019ca091-87c5-74a4-95d6-6ec3b7e5163d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ca091-87c5-718c-b38a-92721ba99182" xlink:to="loc_us-gaap_CommercialPaperMember_019ca091-87c5-74a4-95d6-6ec3b7e5163d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumAmountOutstandingDuringPeriod_019ca091-87c5-7ffb-b9e0-48eac567a9ed" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumAmountOutstandingDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ca091-87c5-76f9-b33f-ddca767f82b2" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumAmountOutstandingDuringPeriod_019ca091-87c5-7ffb-b9e0-48eac567a9ed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityAverageOutstandingAmount_019ca091-87c5-744a-af5e-e3db353a352d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityAverageOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ca091-87c5-76f9-b33f-ddca767f82b2" xlink:to="loc_us-gaap_LineOfCreditFacilityAverageOutstandingAmount_019ca091-87c5-744a-af5e-e3db353a352d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateDuringPeriod_019ca091-87c5-7f14-8fc6-30e93cb1f2c7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ca091-87c5-76f9-b33f-ddca767f82b2" xlink:to="loc_us-gaap_DebtInstrumentInterestRateDuringPeriod_019ca091-87c5-7f14-8fc6-30e93cb1f2c7" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/DebtObligationsCommercialPaperProgramandAdditionalLettersofCreditNarrativeDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#DebtObligationsCommercialPaperProgramandAdditionalLettersofCreditNarrativeDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/DebtObligationsCommercialPaperProgramandAdditionalLettersofCreditNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-766f-ba59-2079c469cde7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019ca091-87c5-7004-adb6-26981702987a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-766f-ba59-2079c469cde7" xlink:to="loc_us-gaap_DebtInstrumentTable_019ca091-87c5-7004-adb6-26981702987a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019ca091-87c5-7e3e-b517-b9ef19a11245" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ca091-87c5-7004-adb6-26981702987a" xlink:to="loc_us-gaap_DebtInstrumentAxis_019ca091-87c5-7e3e-b517-b9ef19a11245" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7e3e-b517-b9ef19a11245_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ca091-87c5-7e3e-b517-b9ef19a11245" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7e3e-b517-b9ef19a11245_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7daa-88d4-a34eaaba4bb4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019ca091-87c5-7e3e-b517-b9ef19a11245" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7daa-88d4-a34eaaba4bb4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_CommercialPaperProgramMember_019ca091-87c5-75bb-97c8-cab79a125666" xlink:href="pwr-20260331.xsd#pwr_CommercialPaperProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7daa-88d4-a34eaaba4bb4" xlink:to="loc_pwr_CommercialPaperProgramMember_019ca091-87c5-75bb-97c8-cab79a125666" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_LettersOfCreditOutsideOfTheSeniorCreditFacilityMember_019ca091-87c5-7fdd-a308-cf39abf69509" xlink:href="pwr-20260331.xsd#pwr_LettersOfCreditOutsideOfTheSeniorCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019ca091-87c5-7daa-88d4-a34eaaba4bb4" xlink:to="loc_pwr_LettersOfCreditOutsideOfTheSeniorCreditFacilityMember_019ca091-87c5-7fdd-a308-cf39abf69509" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019dd9cc-095d-79a1-acf6-c44ee80fc0e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ca091-87c5-7004-adb6-26981702987a" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019dd9cc-095d-79a1-acf6-c44ee80fc0e4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019dd9cc-095d-79a1-acf6-c44ee80fc0e4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019dd9cc-095d-79a1-acf6-c44ee80fc0e4" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019dd9cc-095d-79a1-acf6-c44ee80fc0e4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019dd9cc-095d-7220-b73b-68650a0f1b6f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019dd9cc-095d-79a1-acf6-c44ee80fc0e4" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019dd9cc-095d-7220-b73b-68650a0f1b6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_019ca091-87c5-79d6-b7a3-b0d3a3afc924" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dd9cc-095d-7220-b73b-68650a0f1b6f" xlink:to="loc_us-gaap_CommercialPaperMember_019ca091-87c5-79d6-b7a3-b0d3a3afc924" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaper_019ca091-87c5-70fe-bdbb-921e65832c3a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialPaper"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-766f-ba59-2079c469cde7" xlink:to="loc_us-gaap_CommercialPaper_019ca091-87c5-70fe-bdbb-921e65832c3a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_DebtWeightedAverageTerm_019dacd4-c02e-7ec9-a7f8-33a8661ebc17" xlink:href="pwr-20260331.xsd#pwr_DebtWeightedAverageTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-766f-ba59-2079c469cde7" xlink:to="loc_pwr_DebtWeightedAverageTerm_019dacd4-c02e-7ec9-a7f8-33a8661ebc17" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_019dacd4-98c2-775b-baf4-113e1f08ef46" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ca091-87c5-766f-ba59-2079c469cde7" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_019dacd4-98c2-775b-baf4-113e1f08ef46" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/EquityNarrativeDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#EquityNarrativeDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/EquityNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019ca091-87c5-77f8-9efe-b3b669bec124" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityClassOfTreasuryStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfTreasuryStockTable_019ca091-87c5-7e39-821b-1e1e6b86a2c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfTreasuryStockTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019ca091-87c5-77f8-9efe-b3b669bec124" xlink:to="loc_us-gaap_ClassOfTreasuryStockTable_019ca091-87c5-7e39-821b-1e1e6b86a2c0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramAxis_019ca091-87c5-79d4-8e2f-0646b5304f8f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ShareRepurchaseProgramAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfTreasuryStockTable_019ca091-87c5-7e39-821b-1e1e6b86a2c0" xlink:to="loc_srt_ShareRepurchaseProgramAxis_019ca091-87c5-79d4-8e2f-0646b5304f8f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_019ca091-87c5-79d4-8e2f-0646b5304f8f_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ShareRepurchaseProgramAxis_019ca091-87c5-79d4-8e2f-0646b5304f8f" xlink:to="loc_srt_ShareRepurchaseProgramDomain_019ca091-87c5-79d4-8e2f-0646b5304f8f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_019ca091-87c5-70fd-9972-f7624e49b1b7" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ShareRepurchaseProgramAxis_019ca091-87c5-79d4-8e2f-0646b5304f8f" xlink:to="loc_srt_ShareRepurchaseProgramDomain_019ca091-87c5-70fd-9972-f7624e49b1b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_A2023RepurchaseProgramMember_019ca091-87c5-7a3c-9aeb-30f1245d6145" xlink:href="pwr-20260331.xsd#pwr_A2023RepurchaseProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ShareRepurchaseProgramDomain_019ca091-87c5-70fd-9972-f7624e49b1b7" xlink:to="loc_pwr_A2023RepurchaseProgramMember_019ca091-87c5-7a3c-9aeb-30f1245d6145" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StockRepurchaseProgramAuthorizedAmount1_019ca091-87c5-7ff0-ab50-16c9b85a72c9" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StockRepurchaseProgramAuthorizedAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019ca091-87c5-77f8-9efe-b3b669bec124" xlink:to="loc_srt_StockRepurchaseProgramAuthorizedAmount1_019ca091-87c5-7ff0-ab50-16c9b85a72c9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_019ca091-87c5-7dbc-9b66-e2bf7022e72a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019ca091-87c5-77f8-9efe-b3b669bec124" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_019ca091-87c5-7dbc-9b66-e2bf7022e72a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRepurchaseOfCommonStock_019ca091-87c5-7a55-bde7-536c1f1e9d10" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsForRepurchaseOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019ca091-87c5-77f8-9efe-b3b669bec124" xlink:to="loc_us-gaap_PaymentsForRepurchaseOfCommonStock_019ca091-87c5-7a55-bde7-536c1f1e9d10" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_019ca091-87c5-7e6e-880b-60a8d02d05d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_019ca091-87c5-77f8-9efe-b3b669bec124" xlink:to="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_019ca091-87c5-7e6e-880b-60a8d02d05d6" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/StockBasedCompensationSummaryofPSUsandRSUstobeSettledinCommonStockActivityDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#StockBasedCompensationSummaryofPSUsandRSUstobeSettledinCommonStockActivityDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/StockBasedCompensationSummaryofPSUsandRSUstobeSettledinCommonStockActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ca091-87c5-760c-b084-7b58ae3d3655" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ca091-87c5-7f11-bfa3-cca93d3bf78c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ca091-87c5-760c-b084-7b58ae3d3655" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ca091-87c5-7f11-bfa3-cca93d3bf78c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ca091-87c5-7971-99d9-17ba375b5948" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ca091-87c5-7f11-bfa3-cca93d3bf78c" xlink:to="loc_us-gaap_AwardTypeAxis_019ca091-87c5-7971-99d9-17ba375b5948" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ca091-87c5-7971-99d9-17ba375b5948_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ca091-87c5-7971-99d9-17ba375b5948" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ca091-87c5-7971-99d9-17ba375b5948_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ca091-87c5-70c9-b4d8-c71307ddff06" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ca091-87c5-7971-99d9-17ba375b5948" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ca091-87c5-70c9-b4d8-c71307ddff06" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_RestrictedStockUnitsToBeSettledInCommonStockMember_019ca091-87c5-7d2a-9277-fdced94c085c" xlink:href="pwr-20260331.xsd#pwr_RestrictedStockUnitsToBeSettledInCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ca091-87c5-70c9-b4d8-c71307ddff06" xlink:to="loc_pwr_RestrictedStockUnitsToBeSettledInCommonStockMember_019ca091-87c5-7d2a-9277-fdced94c085c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_PerformanceStockUnitsPSUsMember_019ca091-87c5-7ae9-96bc-fba30b94329c" xlink:href="pwr-20260331.xsd#pwr_PerformanceStockUnitsPSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ca091-87c5-70c9-b4d8-c71307ddff06" xlink:to="loc_pwr_PerformanceStockUnitsPSUsMember_019ca091-87c5-7ae9-96bc-fba30b94329c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ca091-87c5-7022-9c19-57bbe2b7ef84" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ca091-87c5-760c-b084-7b58ae3d3655" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ca091-87c5-7022-9c19-57bbe2b7ef84" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019ca091-87c5-7e28-8ecb-59f808266c23" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ca091-87c5-7022-9c19-57bbe2b7ef84" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019ca091-87c5-7e28-8ecb-59f808266c23" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019ca091-87c5-7d93-9eb0-9f03a50a7696" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ca091-87c5-7022-9c19-57bbe2b7ef84" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019ca091-87c5-7d93-9eb0-9f03a50a7696" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019ca091-87c5-7234-ac70-031548f491e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ca091-87c5-7022-9c19-57bbe2b7ef84" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019ca091-87c5-7234-ac70-031548f491e1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019ca091-87c5-75f8-9864-409ae0d4f8ce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ca091-87c5-7022-9c19-57bbe2b7ef84" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019ca091-87c5-75f8-9864-409ae0d4f8ce" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019ca091-87c5-706e-ba74-c0b0acd6d258" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ca091-87c5-73b0-afcb-65462ed4e31b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ca091-87c5-760c-b084-7b58ae3d3655" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ca091-87c5-73b0-afcb-65462ed4e31b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019ca091-87c5-7999-80bf-c4f2170d6c40" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ca091-87c5-73b0-afcb-65462ed4e31b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019ca091-87c5-7999-80bf-c4f2170d6c40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019ca091-87c5-7fc4-8721-15faee0ca471" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ca091-87c5-73b0-afcb-65462ed4e31b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019ca091-87c5-7fc4-8721-15faee0ca471" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019ca091-87c5-79c1-a831-3d4cf6271fa0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ca091-87c5-73b0-afcb-65462ed4e31b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019ca091-87c5-79c1-a831-3d4cf6271fa0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019ca091-87c5-7548-9f6f-fc786ab72f87" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ca091-87c5-73b0-afcb-65462ed4e31b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019ca091-87c5-7548-9f6f-fc786ab72f87" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019ca091-87c5-77b1-ac18-cf8d113df715" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/StockBasedCompensationAdditionalInformationDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#StockBasedCompensationAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/StockBasedCompensationAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ca091-87c5-78fa-9d1b-22fba5fc0abe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ca091-87c5-7455-9cc6-f7daeaf7b7bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ca091-87c5-78fa-9d1b-22fba5fc0abe" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ca091-87c5-7455-9cc6-f7daeaf7b7bd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ca091-87c5-79c1-97e9-614c612ee2af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ca091-87c5-7455-9cc6-f7daeaf7b7bd" xlink:to="loc_us-gaap_AwardTypeAxis_019ca091-87c5-79c1-97e9-614c612ee2af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ca091-87c5-79c1-97e9-614c612ee2af_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ca091-87c5-79c1-97e9-614c612ee2af" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ca091-87c5-79c1-97e9-614c612ee2af_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ca091-87c5-7d65-8b89-3f8c93002f78" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ca091-87c5-79c1-97e9-614c612ee2af" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ca091-87c5-7d65-8b89-3f8c93002f78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_RestrictedStockUnitsToBeSettledInCommonStockMember_019ca091-87c5-7f74-bc0b-6955b1b31388" xlink:href="pwr-20260331.xsd#pwr_RestrictedStockUnitsToBeSettledInCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ca091-87c5-7d65-8b89-3f8c93002f78" xlink:to="loc_pwr_RestrictedStockUnitsToBeSettledInCommonStockMember_019ca091-87c5-7f74-bc0b-6955b1b31388" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_PerformanceStockUnitsPSUsMember_019ca091-87c5-7b4a-8627-ea9cb050871b" xlink:href="pwr-20260331.xsd#pwr_PerformanceStockUnitsPSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ca091-87c5-7d65-8b89-3f8c93002f78" xlink:to="loc_pwr_PerformanceStockUnitsPSUsMember_019ca091-87c5-7b4a-8627-ea9cb050871b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue_019ca091-87c5-7168-ab7c-b3dab973c373" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ca091-87c5-78fa-9d1b-22fba5fc0abe" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue_019ca091-87c5-7168-ab7c-b3dab973c373" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_019ca091-87c5-76f2-8d53-ceea6a1aff2a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ca091-87c5-78fa-9d1b-22fba5fc0abe" xlink:to="loc_us-gaap_ShareBasedCompensation_019ca091-87c5-76f2-8d53-ceea6a1aff2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_019ca091-87c5-73fc-9b10-d46c08014cad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ca091-87c5-78fa-9d1b-22fba5fc0abe" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_019ca091-87c5-73fc-9b10-d46c08014cad" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019ca091-87c5-7b2a-b73a-4ea49f327aa8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ca091-87c5-78fa-9d1b-22fba5fc0abe" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019ca091-87c5-7b2a-b73a-4ea49f327aa8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_019ca091-87c5-7302-8e2f-156cea0511c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ca091-87c5-78fa-9d1b-22fba5fc0abe" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_019ca091-87c5-7302-8e2f-156cea0511c2" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/StockBasedCompensationGrantDateFairValueforAwardsofPerformanceUnitsInputsDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#StockBasedCompensationGrantDateFairValueforAwardsofPerformanceUnitsInputsDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/StockBasedCompensationGrantDateFairValueforAwardsofPerformanceUnitsInputsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ca091-87c5-79f5-9834-b447045c3eec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ca091-87c5-7439-8c4b-eeeb0a71019e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ca091-87c5-79f5-9834-b447045c3eec" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ca091-87c5-7439-8c4b-eeeb0a71019e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ca091-87c5-78b5-bdfc-ad5f1a604f4c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ca091-87c5-7439-8c4b-eeeb0a71019e" xlink:to="loc_us-gaap_AwardTypeAxis_019ca091-87c5-78b5-bdfc-ad5f1a604f4c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ca091-87c5-78b5-bdfc-ad5f1a604f4c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ca091-87c5-78b5-bdfc-ad5f1a604f4c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ca091-87c5-78b5-bdfc-ad5f1a604f4c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ca091-87c5-7851-a17d-1c2c0fdb65e0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ca091-87c5-78b5-bdfc-ad5f1a604f4c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ca091-87c5-7851-a17d-1c2c0fdb65e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_PerformanceStockUnitsPSUsMember_019ca091-87c5-7946-b33c-e3a43ed22cd7" xlink:href="pwr-20260331.xsd#pwr_PerformanceStockUnitsPSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ca091-87c5-7851-a17d-1c2c0fdb65e0" xlink:to="loc_pwr_PerformanceStockUnitsPSUsMember_019ca091-87c5-7946-b33c-e3a43ed22cd7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharePrice_019ca091-87c5-727e-8628-3e5e51bf29d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ca091-87c5-79f5-9834-b447045c3eec" xlink:to="loc_us-gaap_SharePrice_019ca091-87c5-727e-8628-3e5e51bf29d9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_019ca091-87c5-7387-867f-d10715fb2460" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ca091-87c5-79f5-9834-b447045c3eec" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_019ca091-87c5-7387-867f-d10715fb2460" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_019ca091-87c5-7c8e-b435-1c72f8049a06" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ca091-87c5-79f5-9834-b447045c3eec" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_019ca091-87c5-7c8e-b435-1c72f8049a06" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_019ca091-87c5-7b1d-b1fb-2850878e1266" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ca091-87c5-79f5-9834-b447045c3eec" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_019ca091-87c5-7b1d-b1fb-2850878e1266" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/CommitmentsandContingenciesSilveradoWildfireMatterDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#CommitmentsandContingenciesSilveradoWildfireMatterDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/CommitmentsandContingenciesSilveradoWildfireMatterDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_019ca091-87c5-7d3f-b8e2-9b2ef8809231" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_019ca091-87c5-70c4-b60c-8d162bf908a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_019ca091-87c5-7d3f-b8e2-9b2ef8809231" xlink:to="loc_us-gaap_LossContingenciesTable_019ca091-87c5-70c4-b60c-8d162bf908a4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019ca091-87c5-76b3-b8e0-9494baa50e88" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019ca091-87c5-70c4-b60c-8d162bf908a4" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019ca091-87c5-76b3-b8e0-9494baa50e88" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_019ca091-87c5-76b3-b8e0-9494baa50e88_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019ca091-87c5-76b3-b8e0-9494baa50e88" xlink:to="loc_us-gaap_LossContingencyNatureDomain_019ca091-87c5-76b3-b8e0-9494baa50e88_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_019ca091-87c5-732d-afce-33815272f4f3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019ca091-87c5-76b3-b8e0-9494baa50e88" xlink:to="loc_us-gaap_LossContingencyNatureDomain_019ca091-87c5-732d-afce-33815272f4f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_SilveradoWildfireMember_019ca091-87c5-7429-9aec-5159aedca3c2" xlink:href="pwr-20260331.xsd#pwr_SilveradoWildfireMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_019ca091-87c5-732d-afce-33815272f4f3" xlink:to="loc_pwr_SilveradoWildfireMember_019ca091-87c5-7429-9aec-5159aedca3c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_NumberOfSubsidiariesSubjectToLawsuits_019ca091-87c5-795d-98a8-e10c1189ee15" xlink:href="pwr-20260331.xsd#pwr_NumberOfSubsidiariesSubjectToLawsuits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019ca091-87c5-7d3f-b8e2-9b2ef8809231" xlink:to="loc_pwr_NumberOfSubsidiariesSubjectToLawsuits_019ca091-87c5-795d-98a8-e10c1189ee15" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_DamagedLandArea_019ca091-87c5-730d-86e4-c7f6f3a00179" xlink:href="pwr-20260331.xsd#pwr_DamagedLandArea"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019ca091-87c5-7d3f-b8e2-9b2ef8809231" xlink:to="loc_pwr_DamagedLandArea_019ca091-87c5-730d-86e4-c7f6f3a00179" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_PoleReplacementPeriodBeforeFire_019ca091-87c5-7901-a8bf-e230e64dbd0b" xlink:href="pwr-20260331.xsd#pwr_PoleReplacementPeriodBeforeFire"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019ca091-87c5-7d3f-b8e2-9b2ef8809231" xlink:to="loc_pwr_PoleReplacementPeriodBeforeFire_019ca091-87c5-7901-a8bf-e230e64dbd0b" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/CommitmentsandContingenciesInsuranceDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#CommitmentsandContingenciesInsuranceDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/CommitmentsandContingenciesInsuranceDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pwr_CommitmentAndContingenciesLineItems_019ca091-87c5-714b-894d-24300c127515" xlink:href="pwr-20260331.xsd#pwr_CommitmentAndContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_CommitmentAndContingenciesTable_019ca091-87c5-734d-918c-b813f30c9738" xlink:href="pwr-20260331.xsd#pwr_CommitmentAndContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pwr_CommitmentAndContingenciesLineItems_019ca091-87c5-714b-894d-24300c127515" xlink:to="loc_pwr_CommitmentAndContingenciesTable_019ca091-87c5-734d-918c-b813f30c9738" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019ca091-87c5-7440-8ffe-3215fe436cc2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pwr_CommitmentAndContingenciesTable_019ca091-87c5-734d-918c-b813f30c9738" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019ca091-87c5-7440-8ffe-3215fe436cc2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_019ca091-87c5-7440-8ffe-3215fe436cc2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019ca091-87c5-7440-8ffe-3215fe436cc2" xlink:to="loc_us-gaap_LossContingencyNatureDomain_019ca091-87c5-7440-8ffe-3215fe436cc2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_019ca091-87c5-77a9-862a-89e5bb007fa1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019ca091-87c5-7440-8ffe-3215fe436cc2" xlink:to="loc_us-gaap_LossContingencyNatureDomain_019ca091-87c5-77a9-862a-89e5bb007fa1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_EmployersLiabilityWorkersCompensationAutoLiabilityGeneralLiabilityAndGroupHealthCareClaimsMember_019ca091-87c5-7062-a118-b13d1abf61c0" xlink:href="pwr-20260331.xsd#pwr_EmployersLiabilityWorkersCompensationAutoLiabilityGeneralLiabilityAndGroupHealthCareClaimsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_019ca091-87c5-77a9-862a-89e5bb007fa1" xlink:to="loc_pwr_EmployersLiabilityWorkersCompensationAutoLiabilityGeneralLiabilityAndGroupHealthCareClaimsMember_019ca091-87c5-7062-a118-b13d1abf61c0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_InsuranceTypeAxis_019ca091-87c5-7c0b-bf7d-a138a2de1bbd" xlink:href="pwr-20260331.xsd#pwr_InsuranceTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pwr_CommitmentAndContingenciesTable_019ca091-87c5-734d-918c-b813f30c9738" xlink:to="loc_pwr_InsuranceTypeAxis_019ca091-87c5-7c0b-bf7d-a138a2de1bbd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_InsuranceTypeDomain_019ca091-87c5-7c0b-bf7d-a138a2de1bbd_default" xlink:href="pwr-20260331.xsd#pwr_InsuranceTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_pwr_InsuranceTypeAxis_019ca091-87c5-7c0b-bf7d-a138a2de1bbd" xlink:to="loc_pwr_InsuranceTypeDomain_019ca091-87c5-7c0b-bf7d-a138a2de1bbd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_InsuranceTypeDomain_019ca091-87c5-7efd-90a9-afb60e37a38c" xlink:href="pwr-20260331.xsd#pwr_InsuranceTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_pwr_InsuranceTypeAxis_019ca091-87c5-7c0b-bf7d-a138a2de1bbd" xlink:to="loc_pwr_InsuranceTypeDomain_019ca091-87c5-7efd-90a9-afb60e37a38c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_GeneralAndAutoLiabilityInsuranceMember_019ca091-87c5-79a2-b0df-612aeecd990e" xlink:href="pwr-20260331.xsd#pwr_GeneralAndAutoLiabilityInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pwr_InsuranceTypeDomain_019ca091-87c5-7efd-90a9-afb60e37a38c" xlink:to="loc_pwr_GeneralAndAutoLiabilityInsuranceMember_019ca091-87c5-79a2-b0df-612aeecd990e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_DeductibleAndAdditionalRetentionAmountForLiabilityProgramsMaximum_019ca091-87c5-7404-9a0f-57976ffa2848" xlink:href="pwr-20260331.xsd#pwr_DeductibleAndAdditionalRetentionAmountForLiabilityProgramsMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pwr_CommitmentAndContingenciesLineItems_019ca091-87c5-714b-894d-24300c127515" xlink:to="loc_pwr_DeductibleAndAdditionalRetentionAmountForLiabilityProgramsMaximum_019ca091-87c5-7404-9a0f-57976ffa2848" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_019ca091-87c5-7e3e-9461-32666ef81455" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pwr_CommitmentAndContingenciesLineItems_019ca091-87c5-714b-894d-24300c127515" xlink:to="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_019ca091-87c5-7e3e-9461-32666ef81455" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_019ca091-87c5-7092-a9af-fad9bd6fe335" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pwr_CommitmentAndContingenciesLineItems_019ca091-87c5-714b-894d-24300c127515" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_019ca091-87c5-7092-a9af-fad9bd6fe335" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InsuranceSettlementsReceivable_019ca091-87c5-797a-8c97-52f8b254d567" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InsuranceSettlementsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pwr_CommitmentAndContingenciesLineItems_019ca091-87c5-714b-894d-24300c127515" xlink:to="loc_us-gaap_InsuranceSettlementsReceivable_019ca091-87c5-797a-8c97-52f8b254d567" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InsuranceSettlementsReceivableCurrent_019ca091-87c5-76f0-9a5c-312daa01d976" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InsuranceSettlementsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pwr_CommitmentAndContingenciesLineItems_019ca091-87c5-714b-894d-24300c127515" xlink:to="loc_us-gaap_InsuranceSettlementsReceivableCurrent_019ca091-87c5-76f0-9a5c-312daa01d976" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InsuranceSettlementsReceivableNoncurrent_019ca091-87c5-7473-961e-42ea88b79e4d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InsuranceSettlementsReceivableNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pwr_CommitmentAndContingenciesLineItems_019ca091-87c5-714b-894d-24300c127515" xlink:to="loc_us-gaap_InsuranceSettlementsReceivableNoncurrent_019ca091-87c5-7473-961e-42ea88b79e4d" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/CommitmentsandContingenciesBondsDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#CommitmentsandContingenciesBondsDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/CommitmentsandContingenciesBondsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GuaranteeObligationsLineItems_019ca091-87c5-700f-a1ef-c4e7ede16768" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GuaranteeObligationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGuaranteeObligationsTable_019ca091-87c5-7f50-a14f-c8d6f275b2b1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfGuaranteeObligationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GuaranteeObligationsLineItems_019ca091-87c5-700f-a1ef-c4e7ede16768" xlink:to="loc_us-gaap_ScheduleOfGuaranteeObligationsTable_019ca091-87c5-7f50-a14f-c8d6f275b2b1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GuaranteeObligationsByNatureAxis_019ca091-87c5-7a4c-84c5-0c849b6c6354" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GuaranteeObligationsByNatureAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGuaranteeObligationsTable_019ca091-87c5-7f50-a14f-c8d6f275b2b1" xlink:to="loc_us-gaap_GuaranteeObligationsByNatureAxis_019ca091-87c5-7a4c-84c5-0c849b6c6354" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GuaranteeObligationsNatureDomain_019ca091-87c5-7a4c-84c5-0c849b6c6354_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GuaranteeObligationsNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GuaranteeObligationsByNatureAxis_019ca091-87c5-7a4c-84c5-0c849b6c6354" xlink:to="loc_us-gaap_GuaranteeObligationsNatureDomain_019ca091-87c5-7a4c-84c5-0c849b6c6354_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GuaranteeObligationsNatureDomain_019ca091-87c5-7339-8063-5921fa8ae8a3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GuaranteeObligationsNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GuaranteeObligationsByNatureAxis_019ca091-87c5-7a4c-84c5-0c849b6c6354" xlink:to="loc_us-gaap_GuaranteeObligationsNatureDomain_019ca091-87c5-7339-8063-5921fa8ae8a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceGuaranteeMember_019ca091-87c5-74fd-aefa-bae63dab8744" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceGuaranteeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GuaranteeObligationsNatureDomain_019ca091-87c5-7339-8063-5921fa8ae8a3" xlink:to="loc_us-gaap_PerformanceGuaranteeMember_019ca091-87c5-74fd-aefa-bae63dab8744" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GuaranteeObligationsMaximumExposure_019ca091-87c5-75c5-bfce-f3cd62cd261b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GuaranteeObligationsMaximumExposure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GuaranteeObligationsLineItems_019ca091-87c5-700f-a1ef-c4e7ede16768" xlink:to="loc_us-gaap_GuaranteeObligationsMaximumExposure_019ca091-87c5-75c5-bfce-f3cd62cd261b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/DetailofCertainAccountsAdditionalInformationDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#DetailofCertainAccountsAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/DetailofCertainAccountsAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019ca091-87c5-72d7-a1a2-7475c32a2aab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019ca091-87c5-7338-8514-0c8797b816cb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019ca091-87c5-72d7-a1a2-7475c32a2aab" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019ca091-87c5-7338-8514-0c8797b816cb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019ca091-87c5-725e-b693-63e341a3c58f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019ca091-87c5-7338-8514-0c8797b816cb" xlink:to="loc_srt_StatementGeographicalAxis_019ca091-87c5-725e-b693-63e341a3c58f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019ca091-87c5-725e-b693-63e341a3c58f_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019ca091-87c5-725e-b693-63e341a3c58f" xlink:to="loc_srt_SegmentGeographicalDomain_019ca091-87c5-725e-b693-63e341a3c58f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019ca091-87c5-73f7-bed9-80d83260fa23" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019ca091-87c5-725e-b693-63e341a3c58f" xlink:to="loc_srt_SegmentGeographicalDomain_019ca091-87c5-73f7-bed9-80d83260fa23" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonUsMember_019ca091-87c5-716e-92d9-c02b38a296b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019ca091-87c5-73f7-bed9-80d83260fa23" xlink:to="loc_us-gaap_NonUsMember_019ca091-87c5-716e-92d9-c02b38a296b6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashEquivalentsAtCarryingValue_019ca091-87c5-7f91-9110-c70ff19c88f4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019ca091-87c5-72d7-a1a2-7475c32a2aab" xlink:to="loc_us-gaap_CashEquivalentsAtCarryingValue_019ca091-87c5-7f91-9110-c70ff19c88f4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization_019ca091-87c5-7ccf-8b8a-f62463f1594a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019ca091-87c5-72d7-a1a2-7475c32a2aab" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization_019ca091-87c5-7ccf-8b8a-f62463f1594a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019ca091-87c5-7549-94a6-c83bd964306a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019ca091-87c5-72d7-a1a2-7475c32a2aab" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019ca091-87c5-7549-94a6-c83bd964306a" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/DetailofCertainAccountsCashandCashEquivalentsDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#DetailofCertainAccountsCashandCashEquivalentsDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/DetailofCertainAccountsCashandCashEquivalentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsLineItems_019ca091-87c5-7068-b0c9-12786dc9846a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_019ca091-87c5-7b57-8bbd-ee5a6d091185" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfCashAndCashEquivalentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_019ca091-87c5-7068-b0c9-12786dc9846a" xlink:to="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_019ca091-87c5-7b57-8bbd-ee5a6d091185" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_019ca091-87c5-756a-b481-817638d55ab2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_019ca091-87c5-7b57-8bbd-ee5a6d091185" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_019ca091-87c5-756a-b481-817638d55ab2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019ca091-87c5-756a-b481-817638d55ab2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019ca091-87c5-756a-b481-817638d55ab2" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019ca091-87c5-756a-b481-817638d55ab2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019ca091-87c5-7f08-8c32-b2bfee4ab8e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019ca091-87c5-756a-b481-817638d55ab2" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019ca091-87c5-7f08-8c32-b2bfee4ab8e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_DomesticJointVenturesMember_019ca091-87c5-7a8e-b348-3f10f179c4c7" xlink:href="pwr-20260331.xsd#pwr_DomesticJointVenturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019ca091-87c5-7f08-8c32-b2bfee4ab8e9" xlink:to="loc_pwr_DomesticJointVenturesMember_019ca091-87c5-7a8e-b348-3f10f179c4c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_ForeignJointVenturesMember_019ca091-87c5-7b98-95c8-a410d0c0e974" xlink:href="pwr-20260331.xsd#pwr_ForeignJointVenturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019ca091-87c5-7f08-8c32-b2bfee4ab8e9" xlink:to="loc_pwr_ForeignJointVenturesMember_019ca091-87c5-7b98-95c8-a410d0c0e974" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_InvestmentsInJointVenturesMember_019ca091-87c5-7028-8a78-83eb30cbe452" xlink:href="pwr-20260331.xsd#pwr_InvestmentsInJointVenturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019ca091-87c5-7f08-8c32-b2bfee4ab8e9" xlink:to="loc_pwr_InvestmentsInJointVenturesMember_019ca091-87c5-7028-8a78-83eb30cbe452" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_CaptiveInsuranceCompanyMember_019ca091-87c5-71dc-94a8-25cfa71910be" xlink:href="pwr-20260331.xsd#pwr_CaptiveInsuranceCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019ca091-87c5-7f08-8c32-b2bfee4ab8e9" xlink:to="loc_pwr_CaptiveInsuranceCompanyMember_019ca091-87c5-71dc-94a8-25cfa71910be" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_CashNotHeldByJointVenturesOrCaptiveInsuranceCompanyMember_019ca091-87c5-79b0-8681-f2e8fdf1c7ae" xlink:href="pwr-20260331.xsd#pwr_CashNotHeldByJointVenturesOrCaptiveInsuranceCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019ca091-87c5-7f08-8c32-b2bfee4ab8e9" xlink:to="loc_pwr_CashNotHeldByJointVenturesOrCaptiveInsuranceCompanyMember_019ca091-87c5-79b0-8681-f2e8fdf1c7ae" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019ca091-87c5-7f0f-b2b1-ea7586577321" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_019ca091-87c5-7068-b0c9-12786dc9846a" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019ca091-87c5-7f0f-b2b1-ea7586577321" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/DetailofCertainAccountsIntangibleAssetsDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#DetailofCertainAccountsIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/DetailofCertainAccountsIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pwr_GoodwillAndIntangibleAssetsLineItems_019ca091-87c5-7631-bb0f-3f6ba62494dc" xlink:href="pwr-20260331.xsd#pwr_GoodwillAndIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_GoodwillAndIntangibleAssetsTable_019ca091-87c5-76f4-b3b3-d6cebe752f24" xlink:href="pwr-20260331.xsd#pwr_GoodwillAndIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pwr_GoodwillAndIntangibleAssetsLineItems_019ca091-87c5-7631-bb0f-3f6ba62494dc" xlink:to="loc_pwr_GoodwillAndIntangibleAssetsTable_019ca091-87c5-76f4-b3b3-d6cebe752f24" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ca091-87c5-7d44-b334-b75b71f74efb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pwr_GoodwillAndIntangibleAssetsTable_019ca091-87c5-76f4-b3b3-d6cebe752f24" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ca091-87c5-7d44-b334-b75b71f74efb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ca091-87c5-7d44-b334-b75b71f74efb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ca091-87c5-7d44-b334-b75b71f74efb" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ca091-87c5-7d44-b334-b75b71f74efb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ca091-87c5-790d-9937-af5d5cac40c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ca091-87c5-7d44-b334-b75b71f74efb" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ca091-87c5-790d-9937-af5d5cac40c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_019ca091-87c5-7c0e-9a20-03881f487fbf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ca091-87c5-790d-9937-af5d5cac40c9" xlink:to="loc_us-gaap_CustomerRelationshipsMember_019ca091-87c5-7c0e-9a20-03881f487fbf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OrderOrProductionBacklogMember_019ca091-87c5-7bba-98de-62e5667cc8c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OrderOrProductionBacklogMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ca091-87c5-790d-9937-af5d5cac40c9" xlink:to="loc_us-gaap_OrderOrProductionBacklogMember_019ca091-87c5-7bba-98de-62e5667cc8c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_019ca091-87c5-78e2-a5e4-2d2abb92c96f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ca091-87c5-790d-9937-af5d5cac40c9" xlink:to="loc_us-gaap_TradeNamesMember_019ca091-87c5-78e2-a5e4-2d2abb92c96f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncompeteAgreementsMember_019ca091-87c5-7232-9f8b-1f6669ee9f21" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncompeteAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ca091-87c5-790d-9937-af5d5cac40c9" xlink:to="loc_us-gaap_NoncompeteAgreementsMember_019ca091-87c5-7232-9f8b-1f6669ee9f21" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_019ca091-87c5-75dd-b24a-a9d914d6d4d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ca091-87c5-790d-9937-af5d5cac40c9" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_019ca091-87c5-75dd-b24a-a9d914d6d4d9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pwr_CurriculumMember_019ca091-87c5-7bdc-98ef-1892b1c3225b" xlink:href="pwr-20260331.xsd#pwr_CurriculumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ca091-87c5-790d-9937-af5d5cac40c9" xlink:to="loc_pwr_CurriculumMember_019ca091-87c5-7bdc-98ef-1892b1c3225b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019ca091-87c5-7519-9e5f-b5e2daa8c313" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pwr_GoodwillAndIntangibleAssetsTable_019ca091-87c5-76f4-b3b3-d6cebe752f24" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019ca091-87c5-7519-9e5f-b5e2daa8c313" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019ca091-87c5-7519-9e5f-b5e2daa8c313_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019ca091-87c5-7519-9e5f-b5e2daa8c313" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019ca091-87c5-7519-9e5f-b5e2daa8c313_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019ca091-87c5-7cef-bed3-f6e21b8395ce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019ca091-87c5-7519-9e5f-b5e2daa8c313" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019ca091-87c5-7cef-bed3-f6e21b8395ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LicensingAgreementsMember_019ca091-87c5-7647-80a5-44e74b48e7b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LicensingAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019ca091-87c5-7cef-bed3-f6e21b8395ce" xlink:to="loc_us-gaap_LicensingAgreementsMember_019ca091-87c5-7647-80a5-44e74b48e7b8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019ca091-87c6-70a0-982e-58b9f06e54ba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pwr_GoodwillAndIntangibleAssetsLineItems_019ca091-87c5-7631-bb0f-3f6ba62494dc" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019ca091-87c6-70a0-982e-58b9f06e54ba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019ca091-87c6-7353-8cc3-a44984d255cd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pwr_GoodwillAndIntangibleAssetsLineItems_019ca091-87c5-7631-bb0f-3f6ba62494dc" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019ca091-87c6-7353-8cc3-a44984d255cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019ca091-87c6-7b6d-a29b-f1fb1728f3c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pwr_GoodwillAndIntangibleAssetsLineItems_019ca091-87c5-7631-bb0f-3f6ba62494dc" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019ca091-87c6-7b6d-a29b-f1fb1728f3c6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_019ca091-87c6-7583-a5a6-bfcf49d51030" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pwr_GoodwillAndIntangibleAssetsLineItems_019ca091-87c5-7631-bb0f-3f6ba62494dc" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_019ca091-87c6-7583-a5a6-bfcf49d51030" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_019ca091-87c6-7a17-8c45-3e93d01c0362" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsGrossExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pwr_GoodwillAndIntangibleAssetsLineItems_019ca091-87c5-7631-bb0f-3f6ba62494dc" xlink:to="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_019ca091-87c6-7a17-8c45-3e93d01c0362" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://quantaservices.com/role/SupplementalCashFlowInformationReconciliationofCashCashEquivalentsandRestrictedCashDetails" xlink:type="simple" xlink:href="pwr-20260331.xsd#SupplementalCashFlowInformationReconciliationofCashCashEquivalentsandRestrictedCashDetails"/>
  <link:definitionLink xlink:role="http://quantaservices.com/role/SupplementalCashFlowInformationReconciliationofCashCashEquivalentsandRestrictedCashDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsLineItems_019ca091-87c6-771b-83fe-7c5b631c45cd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_019ca091-87c6-78d3-90d6-82abb33b8205" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfCashAndCashEquivalentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_019ca091-87c6-771b-83fe-7c5b631c45cd" xlink:to="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_019ca091-87c6-78d3-90d6-82abb33b8205" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_019ca091-87c6-7858-a457-9e2b8b3c12b3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_019ca091-87c6-78d3-90d6-82abb33b8205" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_019ca091-87c6-7858-a457-9e2b8b3c12b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_019ca091-87c6-7858-a457-9e2b8b3c12b3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_019ca091-87c6-7858-a457-9e2b8b3c12b3" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_019ca091-87c6-7858-a457-9e2b8b3c12b3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_019ca091-87c6-75df-91de-c92ca6f03915" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_019ca091-87c6-7858-a457-9e2b8b3c12b3" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_019ca091-87c6-75df-91de-c92ca6f03915" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember_019ca091-87c6-75eb-978a-7d090364e972" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_019ca091-87c6-75df-91de-c92ca6f03915" xlink:to="loc_us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember_019ca091-87c6-75eb-978a-7d090364e972" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsMember_019ca091-87c6-766d-be37-038df1a02074" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_019ca091-87c6-75df-91de-c92ca6f03915" xlink:to="loc_us-gaap_OtherAssetsMember_019ca091-87c6-766d-be37-038df1a02074" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019ca091-87c6-7053-9337-4f64a36c4c13" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_019ca091-87c6-771b-83fe-7c5b631c45cd" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019ca091-87c6-7053-9337-4f64a36c4c13" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalents_019ca091-87c6-77a5-b9ec-2f5e1179cc3f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedCashAndCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_019ca091-87c6-771b-83fe-7c5b631c45cd" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalents_019ca091-87c6-77a5-b9ec-2f5e1179cc3f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019ca091-87c6-71cd-80a7-a538dd8b6b49" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_019ca091-87c6-771b-83fe-7c5b631c45cd" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019ca091-87c6-71cd-80a7-a538dd8b6b49" xlink:type="arc" order="2"/>
  </link:definitionLink>
</link:linkbase>
