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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2025 Workiva-->
<!--r:15602bec-d79d-4d3c-8504-4acc99a5d53c,g:f5f985bc-6724-469e-a406-f0b69abf99a6-->
<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://www.muellerindustries.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINEQUITYUnaudited" xlink:type="simple" xlink:href="mli-20250628.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINEQUITYUnaudited"/>
  <link:definitionLink xlink:role="http://www.muellerindustries.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINEQUITYUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_e498be75-1d01-4889-9880-3a2a20e84fff" 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_2bd9d2b7-27da-4a1a-95b1-1240261924ac" 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_e498be75-1d01-4889-9880-3a2a20e84fff" xlink:to="loc_us-gaap_StatementTable_2bd9d2b7-27da-4a1a-95b1-1240261924ac" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_957da190-0bef-4243-ad95-08138cf5d652" 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_2bd9d2b7-27da-4a1a-95b1-1240261924ac" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_957da190-0bef-4243-ad95-08138cf5d652" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_957da190-0bef-4243-ad95-08138cf5d652_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_957da190-0bef-4243-ad95-08138cf5d652" xlink:to="loc_us-gaap_EquityComponentDomain_957da190-0bef-4243-ad95-08138cf5d652_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_1a25fb29-55db-4923-b03d-fc94dc37fe77" 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_957da190-0bef-4243-ad95-08138cf5d652" xlink:to="loc_us-gaap_EquityComponentDomain_1a25fb29-55db-4923-b03d-fc94dc37fe77" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_0a4ec7e4-9c8d-499f-9331-beae3fca2f4f" 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_EquityComponentDomain_1a25fb29-55db-4923-b03d-fc94dc37fe77" xlink:to="loc_us-gaap_CommonStockMember_0a4ec7e4-9c8d-499f-9331-beae3fca2f4f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_469508cf-9272-4e46-90bc-f4f2cec15d0a" 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_EquityComponentDomain_1a25fb29-55db-4923-b03d-fc94dc37fe77" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_469508cf-9272-4e46-90bc-f4f2cec15d0a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_c4b7f115-c29f-4185-bffe-098d52a54911" 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_EquityComponentDomain_1a25fb29-55db-4923-b03d-fc94dc37fe77" xlink:to="loc_us-gaap_RetainedEarningsMember_c4b7f115-c29f-4185-bffe-098d52a54911" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_dfc07043-05b6-4b63-ada6-f92a808126b2" 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_EquityComponentDomain_1a25fb29-55db-4923-b03d-fc94dc37fe77" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_dfc07043-05b6-4b63-ada6-f92a808126b2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_cb7d37ef-bdce-4314-89d4-0a6ff16291d4" 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_EquityComponentDomain_1a25fb29-55db-4923-b03d-fc94dc37fe77" xlink:to="loc_us-gaap_TreasuryStockCommonMember_cb7d37ef-bdce-4314-89d4-0a6ff16291d4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_4b932a38-79a5-48e4-b058-311149dd8e66" 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_1a25fb29-55db-4923-b03d-fc94dc37fe77" xlink:to="loc_us-gaap_NoncontrollingInterestMember_4b932a38-79a5-48e4-b058-311149dd8e66" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d53cab6-ac44-4c37-b584-4c106a4833a2" 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_e498be75-1d01-4889-9880-3a2a20e84fff" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d53cab6-ac44-4c37-b584-4c106a4833a2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_9dcf58ca-c9c4-4fdc-8538-7647e5ddafdd" 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_6d53cab6-ac44-4c37-b584-4c106a4833a2" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_9dcf58ca-c9c4-4fdc-8538-7647e5ddafdd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_efbe2fcf-2e4f-4ecc-8be7-028dc0c29fa6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d53cab6-ac44-4c37-b584-4c106a4833a2" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_efbe2fcf-2e4f-4ecc-8be7-028dc0c29fa6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_9521411e-7886-44f2-916a-c4e7b193ff40" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d53cab6-ac44-4c37-b584-4c106a4833a2" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_9521411e-7886-44f2-916a-c4e7b193ff40" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_58d30e0a-bb66-444f-98dd-9bc6cde6bf9f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d53cab6-ac44-4c37-b584-4c106a4833a2" xlink:to="loc_us-gaap_NetIncomeLoss_58d30e0a-bb66-444f-98dd-9bc6cde6bf9f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Dividends_b69d8d76-6072-4293-b216-46f843d9a773" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Dividends"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d53cab6-ac44-4c37-b584-4c106a4833a2" xlink:to="loc_us-gaap_Dividends_b69d8d76-6072-4293-b216-46f843d9a773" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_af11d266-4319-4bc3-a86b-04a0072f2899" 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_6d53cab6-ac44-4c37-b584-4c106a4833a2" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_af11d266-4319-4bc3-a86b-04a0072f2899" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_8cceee56-7710-4154-818b-ec4fe266c3b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d53cab6-ac44-4c37-b584-4c106a4833a2" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_8cceee56-7710-4154-818b-ec4fe266c3b8" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_e3ba2cc4-10e5-47c2-987a-3fc6a4e88428" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d53cab6-ac44-4c37-b584-4c106a4833a2" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_e3ba2cc4-10e5-47c2-987a-3fc6a4e88428" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross_7d3b6ac2-eb8d-46de-bdd4-2be120b37b70" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d53cab6-ac44-4c37-b584-4c106a4833a2" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross_7d3b6ac2-eb8d-46de-bdd4-2be120b37b70" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_InvestmentInJointVenture_cd3b3faf-5f73-43c4-87ce-39e039d68f36" xlink:href="mli-20250628.xsd#mli_InvestmentInJointVenture"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d53cab6-ac44-4c37-b584-4c106a4833a2" xlink:to="loc_mli_InvestmentInJointVenture_cd3b3faf-5f73-43c4-87ce-39e039d68f36" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_828c4457-a376-4d46-b6fe-d86ac1bd5062" 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_6d53cab6-ac44-4c37-b584-4c106a4833a2" xlink:to="loc_us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_828c4457-a376-4d46-b6fe-d86ac1bd5062" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_1b485612-8792-41d0-9940-ded2cc923015" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d53cab6-ac44-4c37-b584-4c106a4833a2" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_1b485612-8792-41d0-9940-ded2cc923015" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_9054cdf2-ed50-44ad-8f0d-1f157f50bb31" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d53cab6-ac44-4c37-b584-4c106a4833a2" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_9054cdf2-ed50-44ad-8f0d-1f157f50bb31" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_4e50ddc6-22b6-45b7-8312-e84df22be423" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.muellerindustries.com/role/AcquisitionsNarrativeDetails" xlink:type="simple" xlink:href="mli-20250628.xsd#AcquisitionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.muellerindustries.com/role/AcquisitionsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_7e039449-bbf4-4973-8811-3e201f0b8216" 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_be9d7a27-1119-43bb-bcf4-d9595eaf5ff0" 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_7e039449-bbf4-4973-8811-3e201f0b8216" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_be9d7a27-1119-43bb-bcf4-d9595eaf5ff0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_e5ccfebb-7d74-45db-bb97-aefe060d36c9" 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_be9d7a27-1119-43bb-bcf4-d9595eaf5ff0" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_e5ccfebb-7d74-45db-bb97-aefe060d36c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e5ccfebb-7d74-45db-bb97-aefe060d36c9_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_e5ccfebb-7d74-45db-bb97-aefe060d36c9" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e5ccfebb-7d74-45db-bb97-aefe060d36c9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_53526281-3bcb-483d-bfea-7b5c9c53c0cf" 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_e5ccfebb-7d74-45db-bb97-aefe060d36c9" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_53526281-3bcb-483d-bfea-7b5c9c53c0cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_ElkhartProductsCorporationMember_fd6cd345-279b-4be0-a05c-1a1f10ac68f6" xlink:href="mli-20250628.xsd#mli_ElkhartProductsCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_53526281-3bcb-483d-bfea-7b5c9c53c0cf" xlink:to="loc_mli_ElkhartProductsCorporationMember_fd6cd345-279b-4be0-a05c-1a1f10ac68f6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_NehringElectricalWorksCompanyMember_0700c6f9-cad4-4f28-a2e3-44bd4f51d777" xlink:href="mli-20250628.xsd#mli_NehringElectricalWorksCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_53526281-3bcb-483d-bfea-7b5c9c53c0cf" xlink:to="loc_mli_NehringElectricalWorksCompanyMember_0700c6f9-cad4-4f28-a2e3-44bd4f51d777" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_cddfe57a-3322-4c3d-a53c-94c0569fe74e" 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_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_be9d7a27-1119-43bb-bcf4-d9595eaf5ff0" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_cddfe57a-3322-4c3d-a53c-94c0569fe74e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_cddfe57a-3322-4c3d-a53c-94c0569fe74e_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_cddfe57a-3322-4c3d-a53c-94c0569fe74e" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_cddfe57a-3322-4c3d-a53c-94c0569fe74e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_473d5b3d-1abe-46e9-941c-d60f3a26232f" 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_cddfe57a-3322-4c3d-a53c-94c0569fe74e" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_473d5b3d-1abe-46e9-941c-d60f3a26232f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_a15ccd43-bebe-4b07-850c-efd3a8a2be26" 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_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_473d5b3d-1abe-46e9-941c-d60f3a26232f" xlink:to="loc_us-gaap_TradeNamesMember_a15ccd43-bebe-4b07-850c-efd3a8a2be26" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_33cadf7d-229e-4f3c-9e0f-080946452033" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_7e039449-bbf4-4973-8811-3e201f0b8216" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_33cadf7d-229e-4f3c-9e0f-080946452033" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_NumberOfManufacturingLocations_27ac87d1-805d-4fea-a611-05bd07418315" xlink:href="mli-20250628.xsd#mli_NumberOfManufacturingLocations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_7e039449-bbf4-4973-8811-3e201f0b8216" xlink:to="loc_mli_NumberOfManufacturingLocations_27ac87d1-805d-4fea-a611-05bd07418315" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets_e62266b4-d45e-4777-8bdc-26afbf66833d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_7e039449-bbf4-4973-8811-3e201f0b8216" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets_e62266b4-d45e-4777-8bdc-26afbf66833d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_126caaf0-10b8-40fa-a5f4-55f41356ad3f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_7e039449-bbf4-4973-8811-3e201f0b8216" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_126caaf0-10b8-40fa-a5f4-55f41356ad3f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_3e0b424f-adfc-484f-9fbe-57e86bbef899" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_7e039449-bbf4-4973-8811-3e201f0b8216" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_3e0b424f-adfc-484f-9fbe-57e86bbef899" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_a01274dd-0a44-489b-9214-81f5685be8c8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_7e039449-bbf4-4973-8811-3e201f0b8216" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_a01274dd-0a44-489b-9214-81f5685be8c8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther_127c0e80-39ec-4948-82b1-9fd4839139aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_7e039449-bbf4-4973-8811-3e201f0b8216" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther_127c0e80-39ec-4948-82b1-9fd4839139aa" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_3fe83f11-f634-4f00-acb7-ed0c65fdd6bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_7e039449-bbf4-4973-8811-3e201f0b8216" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_3fe83f11-f634-4f00-acb7-ed0c65fdd6bd" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther_c5e0cb50-b443-45c6-907e-0aebfb27208e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_7e039449-bbf4-4973-8811-3e201f0b8216" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther_c5e0cb50-b443-45c6-907e-0aebfb27208e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_2e110b5b-e542-4900-9ee9-b543923ed9e8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_7e039449-bbf4-4973-8811-3e201f0b8216" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_2e110b5b-e542-4900-9ee9-b543923ed9e8" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_4cf874e4-959a-422a-bf79-7dc3e0aeda9f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_7e039449-bbf4-4973-8811-3e201f0b8216" xlink:to="loc_us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_4cf874e4-959a-422a-bf79-7dc3e0aeda9f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefinitelivedIntangibleAssetsAcquired_71607cf3-7133-4909-86bb-dc0c7158f669" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefinitelivedIntangibleAssetsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_7e039449-bbf4-4973-8811-3e201f0b8216" xlink:to="loc_us-gaap_IndefinitelivedIntangibleAssetsAcquired_71607cf3-7133-4909-86bb-dc0c7158f669" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_80e327a2-9014-4fdc-b779-9ea3a808d0b0" 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_7e039449-bbf4-4973-8811-3e201f0b8216" xlink:to="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_80e327a2-9014-4fdc-b779-9ea3a808d0b0" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_2358c7d1-116f-4980-8f9e-efbde7a5b820" 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_7e039449-bbf4-4973-8811-3e201f0b8216" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_2358c7d1-116f-4980-8f9e-efbde7a5b820" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_9dace189-11f4-428e-9449-4595aa1d4ee5" 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_BusinessAcquisitionLineItems_7e039449-bbf4-4973-8811-3e201f0b8216" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_9dace189-11f4-428e-9449-4595aa1d4ee5" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_bf7e1eb3-5937-4f31-b9b8-6594bf192854" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_7e039449-bbf4-4973-8811-3e201f0b8216" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_bf7e1eb3-5937-4f31-b9b8-6594bf192854" xlink:type="arc" order="15"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.muellerindustries.com/role/AcquisitionsCondensedProFormaConsolidatedResultsofOperationsDetails" xlink:type="simple" xlink:href="mli-20250628.xsd#AcquisitionsCondensedProFormaConsolidatedResultsofOperationsDetails"/>
  <link:definitionLink xlink:role="http://www.muellerindustries.com/role/AcquisitionsCondensedProFormaConsolidatedResultsofOperationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_559f86d6-28a7-469e-80c1-d48d0d3b77df" 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_22b4e18b-8db6-46e6-80d6-b09be5225f55" 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_559f86d6-28a7-469e-80c1-d48d0d3b77df" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_22b4e18b-8db6-46e6-80d6-b09be5225f55" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_969f262b-bec4-4292-a063-80600a482f16" 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_22b4e18b-8db6-46e6-80d6-b09be5225f55" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_969f262b-bec4-4292-a063-80600a482f16" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_969f262b-bec4-4292-a063-80600a482f16_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_969f262b-bec4-4292-a063-80600a482f16" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_969f262b-bec4-4292-a063-80600a482f16_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_1648a710-c44d-4b2d-bea3-920d0b747d0a" 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_969f262b-bec4-4292-a063-80600a482f16" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_1648a710-c44d-4b2d-bea3-920d0b747d0a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_NehringElectricalWorksCompanyMember_44656efe-425d-49b0-91f5-97c438a7ef27" xlink:href="mli-20250628.xsd#mli_NehringElectricalWorksCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_1648a710-c44d-4b2d-bea3-920d0b747d0a" xlink:to="loc_mli_NehringElectricalWorksCompanyMember_44656efe-425d-49b0-91f5-97c438a7ef27" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_9dda4fe9-3c9a-402c-ae4e-ec92a74cea97" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionsProFormaRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_559f86d6-28a7-469e-80c1-d48d0d3b77df" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_9dda4fe9-3c9a-402c-ae4e-ec92a74cea97" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_52398fa7-6a42-4dc8-a899-42d61d03f0f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_559f86d6-28a7-469e-80c1-d48d0d3b77df" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_52398fa7-6a42-4dc8-a899-42d61d03f0f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionProFormaEarningsPerShareBasic_3be625f1-5c98-4a9f-9d4b-0a5e8931e71a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionProFormaEarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_559f86d6-28a7-469e-80c1-d48d0d3b77df" xlink:to="loc_us-gaap_BusinessAcquisitionProFormaEarningsPerShareBasic_3be625f1-5c98-4a9f-9d4b-0a5e8931e71a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionProFormaEarningsPerShareDiluted_5170ee47-a3dd-4196-a0fc-64406f456f9a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionProFormaEarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_559f86d6-28a7-469e-80c1-d48d0d3b77df" xlink:to="loc_us-gaap_BusinessAcquisitionProFormaEarningsPerShareDiluted_5170ee47-a3dd-4196-a0fc-64406f456f9a" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.muellerindustries.com/role/SegmentInformationScheduleofDisaggregationofRevenueFromContractswithCustomersDetails" xlink:type="simple" xlink:href="mli-20250628.xsd#SegmentInformationScheduleofDisaggregationofRevenueFromContractswithCustomersDetails"/>
  <link:definitionLink xlink:role="http://www.muellerindustries.com/role/SegmentInformationScheduleofDisaggregationofRevenueFromContractswithCustomersDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_5f80e2d4-f3a7-4135-ad73-2f3fb389d3ef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_65733647-b828-42ee-9397-c04a2e71a0f2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_5f80e2d4-f3a7-4135-ad73-2f3fb389d3ef" xlink:to="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_65733647-b828-42ee-9397-c04a2e71a0f2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_e5c92222-1444-4545-963c-9fecb438323a" 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_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_65733647-b828-42ee-9397-c04a2e71a0f2" xlink:to="loc_srt_ConsolidationItemsAxis_e5c92222-1444-4545-963c-9fecb438323a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_e5c92222-1444-4545-963c-9fecb438323a_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_e5c92222-1444-4545-963c-9fecb438323a" xlink:to="loc_srt_ConsolidationItemsDomain_e5c92222-1444-4545-963c-9fecb438323a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_39c8c0a1-a0de-4fda-a44e-23d4bd8038d3" 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_e5c92222-1444-4545-963c-9fecb438323a" xlink:to="loc_srt_ConsolidationItemsDomain_39c8c0a1-a0de-4fda-a44e-23d4bd8038d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_7803c682-eaf1-4b49-99a0-f07490c50ff7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_39c8c0a1-a0de-4fda-a44e-23d4bd8038d3" xlink:to="loc_us-gaap_OperatingSegmentsMember_7803c682-eaf1-4b49-99a0-f07490c50ff7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntersegmentEliminationMember_216c822a-2ecb-48ef-af19-756bc2d7fef3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntersegmentEliminationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_39c8c0a1-a0de-4fda-a44e-23d4bd8038d3" xlink:to="loc_us-gaap_IntersegmentEliminationMember_216c822a-2ecb-48ef-af19-756bc2d7fef3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_27eca256-2185-4c10-8f90-70de2e2d0c9d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_65733647-b828-42ee-9397-c04a2e71a0f2" xlink:to="loc_srt_ProductOrServiceAxis_27eca256-2185-4c10-8f90-70de2e2d0c9d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_27eca256-2185-4c10-8f90-70de2e2d0c9d_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_27eca256-2185-4c10-8f90-70de2e2d0c9d" xlink:to="loc_srt_ProductsAndServicesDomain_27eca256-2185-4c10-8f90-70de2e2d0c9d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_18ec1a2f-4d09-4f2b-9f62-15ebe8dbd79b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_27eca256-2185-4c10-8f90-70de2e2d0c9d" xlink:to="loc_srt_ProductsAndServicesDomain_18ec1a2f-4d09-4f2b-9f62-15ebe8dbd79b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_TubeAndFittingsMember_117ddc39-9ab2-450b-b4c1-e9f491052b3b" xlink:href="mli-20250628.xsd#mli_TubeAndFittingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_18ec1a2f-4d09-4f2b-9f62-15ebe8dbd79b" xlink:to="loc_mli_TubeAndFittingsMember_117ddc39-9ab2-450b-b4c1-e9f491052b3b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_BrassRodAndForgingsMember_ebeb063f-9c0d-4981-a559-54375c94569e" xlink:href="mli-20250628.xsd#mli_BrassRodAndForgingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_18ec1a2f-4d09-4f2b-9f62-15ebe8dbd79b" xlink:to="loc_mli_BrassRodAndForgingsMember_ebeb063f-9c0d-4981-a559-54375c94569e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_OEMComponentsTubeAndAssembliesMember_a3803b5f-96d5-4b18-89ec-dc9b283a9e2f" xlink:href="mli-20250628.xsd#mli_OEMComponentsTubeAndAssembliesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_18ec1a2f-4d09-4f2b-9f62-15ebe8dbd79b" xlink:to="loc_mli_OEMComponentsTubeAndAssembliesMember_a3803b5f-96d5-4b18-89ec-dc9b283a9e2f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_ValvesAndPlumbingSpecialtiesMember_9dc24a76-1c07-4659-9071-20618d93e5ff" xlink:href="mli-20250628.xsd#mli_ValvesAndPlumbingSpecialtiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_18ec1a2f-4d09-4f2b-9f62-15ebe8dbd79b" xlink:to="loc_mli_ValvesAndPlumbingSpecialtiesMember_9dc24a76-1c07-4659-9071-20618d93e5ff" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_FlexDuctAndOtherHVACComponentsMember_eea49936-a0cb-4da7-9851-b58c48da9531" xlink:href="mli-20250628.xsd#mli_FlexDuctAndOtherHVACComponentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_18ec1a2f-4d09-4f2b-9f62-15ebe8dbd79b" xlink:to="loc_mli_FlexDuctAndOtherHVACComponentsMember_eea49936-a0cb-4da7-9851-b58c48da9531" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_OtherProductsMember_26c44959-35bf-4eb9-ba06-ac6f59a82b26" xlink:href="mli-20250628.xsd#mli_OtherProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_18ec1a2f-4d09-4f2b-9f62-15ebe8dbd79b" xlink:to="loc_mli_OtherProductsMember_26c44959-35bf-4eb9-ba06-ac6f59a82b26" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_8b784d96-ce6c-4085-b4d1-c67debe8d51b" 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_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_65733647-b828-42ee-9397-c04a2e71a0f2" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_8b784d96-ce6c-4085-b4d1-c67debe8d51b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_8b784d96-ce6c-4085-b4d1-c67debe8d51b_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_8b784d96-ce6c-4085-b4d1-c67debe8d51b" xlink:to="loc_us-gaap_SegmentDomain_8b784d96-ce6c-4085-b4d1-c67debe8d51b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_29801a5a-b020-42c0-b2ee-5f76e2672817" 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_8b784d96-ce6c-4085-b4d1-c67debe8d51b" xlink:to="loc_us-gaap_SegmentDomain_29801a5a-b020-42c0-b2ee-5f76e2672817" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_PipingSystemsMember_59883172-d357-48dc-94e8-a3c13738cd3f" xlink:href="mli-20250628.xsd#mli_PipingSystemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_29801a5a-b020-42c0-b2ee-5f76e2672817" xlink:to="loc_mli_PipingSystemsMember_59883172-d357-48dc-94e8-a3c13738cd3f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_IndustrialMetalsMember_7e5ec2e3-c11d-4449-9945-4a5fd9a0fe93" xlink:href="mli-20250628.xsd#mli_IndustrialMetalsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_29801a5a-b020-42c0-b2ee-5f76e2672817" xlink:to="loc_mli_IndustrialMetalsMember_7e5ec2e3-c11d-4449-9945-4a5fd9a0fe93" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_ClimateMember_2f034e52-5b3f-4b71-b3ee-c11b3b0f53b1" xlink:href="mli-20250628.xsd#mli_ClimateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_29801a5a-b020-42c0-b2ee-5f76e2672817" xlink:to="loc_mli_ClimateMember_2f034e52-5b3f-4b71-b3ee-c11b3b0f53b1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_3cd8a8f5-cd1c-4e65-96b1-cd6da90a89b4" 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_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_5f80e2d4-f3a7-4135-ad73-2f3fb389d3ef" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_3cd8a8f5-cd1c-4e65-96b1-cd6da90a89b4" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.muellerindustries.com/role/SegmentInformationScheduleofSegmentInformationDetails" xlink:type="simple" xlink:href="mli-20250628.xsd#SegmentInformationScheduleofSegmentInformationDetails"/>
  <link:definitionLink xlink:role="http://www.muellerindustries.com/role/SegmentInformationScheduleofSegmentInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_3144389f-bcc9-4e90-b22f-38cabfc83296" 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_feb983e4-0af3-4a10-b143-644345af9563" 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_3144389f-bcc9-4e90-b22f-38cabfc83296" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_feb983e4-0af3-4a10-b143-644345af9563" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_c81cfef8-f293-43b1-911e-c769ac5529b5" 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_feb983e4-0af3-4a10-b143-644345af9563" xlink:to="loc_srt_ConsolidationItemsAxis_c81cfef8-f293-43b1-911e-c769ac5529b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_c81cfef8-f293-43b1-911e-c769ac5529b5_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_c81cfef8-f293-43b1-911e-c769ac5529b5" xlink:to="loc_srt_ConsolidationItemsDomain_c81cfef8-f293-43b1-911e-c769ac5529b5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_23fd53fd-45a9-4b33-ad44-8ebdf42880dc" 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_c81cfef8-f293-43b1-911e-c769ac5529b5" xlink:to="loc_srt_ConsolidationItemsDomain_23fd53fd-45a9-4b33-ad44-8ebdf42880dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_6ef8d05d-4074-4af7-bd73-fe2e159dc901" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_23fd53fd-45a9-4b33-ad44-8ebdf42880dc" xlink:to="loc_us-gaap_OperatingSegmentsMember_6ef8d05d-4074-4af7-bd73-fe2e159dc901" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntersegmentEliminationMember_4818c7bf-2aba-468c-83c6-ce903e0ec160" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntersegmentEliminationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_23fd53fd-45a9-4b33-ad44-8ebdf42880dc" xlink:to="loc_us-gaap_IntersegmentEliminationMember_4818c7bf-2aba-468c-83c6-ce903e0ec160" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_1a5ced1d-4efb-445b-9f89-e3bf493044cb" 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_23fd53fd-45a9-4b33-ad44-8ebdf42880dc" xlink:to="loc_us-gaap_CorporateNonSegmentMember_1a5ced1d-4efb-445b-9f89-e3bf493044cb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaterialReconcilingItemsMember_1df7fbd2-f198-4047-9253-5b5053867bb4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MaterialReconcilingItemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_23fd53fd-45a9-4b33-ad44-8ebdf42880dc" xlink:to="loc_us-gaap_MaterialReconcilingItemsMember_1df7fbd2-f198-4047-9253-5b5053867bb4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_7cc76b6b-6e6a-476a-ae23-e803cec2e227" 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_feb983e4-0af3-4a10-b143-644345af9563" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_7cc76b6b-6e6a-476a-ae23-e803cec2e227" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_7cc76b6b-6e6a-476a-ae23-e803cec2e227_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_7cc76b6b-6e6a-476a-ae23-e803cec2e227" xlink:to="loc_us-gaap_SegmentDomain_7cc76b6b-6e6a-476a-ae23-e803cec2e227_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_dd7c01c3-6370-4033-a39a-39167f26b4fc" 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_7cc76b6b-6e6a-476a-ae23-e803cec2e227" xlink:to="loc_us-gaap_SegmentDomain_dd7c01c3-6370-4033-a39a-39167f26b4fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_PipingSystemsMember_63d803ce-e052-4d94-b717-db120cea95c2" xlink:href="mli-20250628.xsd#mli_PipingSystemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_dd7c01c3-6370-4033-a39a-39167f26b4fc" xlink:to="loc_mli_PipingSystemsMember_63d803ce-e052-4d94-b717-db120cea95c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_IndustrialMetalsMember_4492b5a4-f5fe-4def-88b8-6b91bde6a8bb" xlink:href="mli-20250628.xsd#mli_IndustrialMetalsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_dd7c01c3-6370-4033-a39a-39167f26b4fc" xlink:to="loc_mli_IndustrialMetalsMember_4492b5a4-f5fe-4def-88b8-6b91bde6a8bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_ClimateMember_12276e2c-68c1-4389-821d-a62120965e0e" xlink:href="mli-20250628.xsd#mli_ClimateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_dd7c01c3-6370-4033-a39a-39167f26b4fc" xlink:to="loc_mli_ClimateMember_12276e2c-68c1-4389-821d-a62120965e0e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_757c6e7f-8c32-449b-93e1-120cd5a9b5a5" 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_3144389f-bcc9-4e90-b22f-38cabfc83296" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_757c6e7f-8c32-449b-93e1-120cd5a9b5a5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ManufacturingCosts_a1bdad1e-5ec5-4634-bb9b-ca9f87066a7e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ManufacturingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3144389f-bcc9-4e90-b22f-38cabfc83296" xlink:to="loc_us-gaap_ManufacturingCosts_a1bdad1e-5ec5-4634-bb9b-ca9f87066a7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpense_a2c79f15-a38c-420c-b611-2e918b0361fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingAndMarketingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3144389f-bcc9-4e90-b22f-38cabfc83296" xlink:to="loc_us-gaap_SellingAndMarketingExpense_a2c79f15-a38c-420c-b611-2e918b0361fb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductionAndDistributionCosts_433dff8e-e52b-4470-ae1d-1df86c871df9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProductionAndDistributionCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3144389f-bcc9-4e90-b22f-38cabfc83296" xlink:to="loc_us-gaap_ProductionAndDistributionCosts_433dff8e-e52b-4470-ae1d-1df86c871df9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_4f9867de-56f7-4cbf-bb97-f7e8f54439e6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3144389f-bcc9-4e90-b22f-38cabfc83296" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_4f9867de-56f7-4cbf-bb97-f7e8f54439e6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_OperatingIncomeLossExcludingCorporate_a152bc84-1b88-4fdf-bd5c-e775fe550358" xlink:href="mli-20250628.xsd#mli_OperatingIncomeLossExcludingCorporate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3144389f-bcc9-4e90-b22f-38cabfc83296" xlink:to="loc_mli_OperatingIncomeLossExcludingCorporate_a152bc84-1b88-4fdf-bd5c-e775fe550358" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_0caff3d7-0f82-457a-9d8c-0d34e56d9b0b" 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_3144389f-bcc9-4e90-b22f-38cabfc83296" xlink:to="loc_us-gaap_OperatingIncomeLoss_0caff3d7-0f82-457a-9d8c-0d34e56d9b0b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_585b6cec-4676-4379-b103-1f4d1d167653" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3144389f-bcc9-4e90-b22f-38cabfc83296" xlink:to="loc_us-gaap_InterestExpenseNonoperating_585b6cec-4676-4379-b103-1f4d1d167653" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInterest_8969f33a-5b55-480b-be79-ee21efdb2499" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentIncomeInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3144389f-bcc9-4e90-b22f-38cabfc83296" xlink:to="loc_us-gaap_InvestmentIncomeInterest_8969f33a-5b55-480b-be79-ee21efdb2499" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnInvestments_6b630f92-1f6f-4f5c-b38e-7f4601fcff11" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3144389f-bcc9-4e90-b22f-38cabfc83296" xlink:to="loc_us-gaap_GainLossOnInvestments_6b630f92-1f6f-4f5c-b38e-7f4601fcff11" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_2c2c897a-570d-4af9-9f67-38926e9d2595" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3144389f-bcc9-4e90-b22f-38cabfc83296" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_2c2c897a-570d-4af9-9f67-38926e9d2595" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_e7839876-328b-4fa7-a617-ba27e49e38be" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3144389f-bcc9-4e90-b22f-38cabfc83296" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_e7839876-328b-4fa7-a617-ba27e49e38be" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.muellerindustries.com/role/SegmentInformationOthersegmentdisclosuresDetails" xlink:type="simple" xlink:href="mli-20250628.xsd#SegmentInformationOthersegmentdisclosuresDetails"/>
  <link:definitionLink xlink:role="http://www.muellerindustries.com/role/SegmentInformationOthersegmentdisclosuresDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_1002bc87-1c16-4f76-a628-7a1ec23a89a0" 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_716f4086-b228-494e-8d6f-c8824613e606" 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_1002bc87-1c16-4f76-a628-7a1ec23a89a0" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_716f4086-b228-494e-8d6f-c8824613e606" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_19378d01-fcd3-4e69-8e85-49cfb6602a47" 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_716f4086-b228-494e-8d6f-c8824613e606" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_19378d01-fcd3-4e69-8e85-49cfb6602a47" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_19378d01-fcd3-4e69-8e85-49cfb6602a47_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_19378d01-fcd3-4e69-8e85-49cfb6602a47" xlink:to="loc_us-gaap_SegmentDomain_19378d01-fcd3-4e69-8e85-49cfb6602a47_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_adc1e743-4fe3-4550-97a7-df08f967926a" 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_19378d01-fcd3-4e69-8e85-49cfb6602a47" xlink:to="loc_us-gaap_SegmentDomain_adc1e743-4fe3-4550-97a7-df08f967926a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_PipingSystemsMember_653c79e8-0307-4613-8e60-074377763210" xlink:href="mli-20250628.xsd#mli_PipingSystemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_adc1e743-4fe3-4550-97a7-df08f967926a" xlink:to="loc_mli_PipingSystemsMember_653c79e8-0307-4613-8e60-074377763210" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_IndustrialMetalsMember_c87011d2-725b-4be7-9e9a-bdab0607405d" xlink:href="mli-20250628.xsd#mli_IndustrialMetalsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_adc1e743-4fe3-4550-97a7-df08f967926a" xlink:to="loc_mli_IndustrialMetalsMember_c87011d2-725b-4be7-9e9a-bdab0607405d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_ClimateMember_324bf551-7283-49c4-9fd9-c219887435e9" xlink:href="mli-20250628.xsd#mli_ClimateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_adc1e743-4fe3-4550-97a7-df08f967926a" xlink:to="loc_mli_ClimateMember_324bf551-7283-49c4-9fd9-c219887435e9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_464d1cdc-78fe-457e-a9cc-dd76b65fb52b" 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_716f4086-b228-494e-8d6f-c8824613e606" xlink:to="loc_srt_ConsolidationItemsAxis_464d1cdc-78fe-457e-a9cc-dd76b65fb52b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_464d1cdc-78fe-457e-a9cc-dd76b65fb52b_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_464d1cdc-78fe-457e-a9cc-dd76b65fb52b" xlink:to="loc_srt_ConsolidationItemsDomain_464d1cdc-78fe-457e-a9cc-dd76b65fb52b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_53969776-1dd2-401e-8db2-8d71d8011aac" 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_464d1cdc-78fe-457e-a9cc-dd76b65fb52b" xlink:to="loc_srt_ConsolidationItemsDomain_53969776-1dd2-401e-8db2-8d71d8011aac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_2c750f56-1844-47fb-ac40-d991af7a5ad6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_53969776-1dd2-401e-8db2-8d71d8011aac" xlink:to="loc_us-gaap_OperatingSegmentsMember_2c750f56-1844-47fb-ac40-d991af7a5ad6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_26789c37-d251-492a-86ce-5c1fc7e4482f" 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_53969776-1dd2-401e-8db2-8d71d8011aac" xlink:to="loc_us-gaap_CorporateNonSegmentMember_26789c37-d251-492a-86ce-5c1fc7e4482f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_9f53f52e-4a22-49ec-a679-f8a9cf0af7af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_1002bc87-1c16-4f76-a628-7a1ec23a89a0" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_9f53f52e-4a22-49ec-a679-f8a9cf0af7af" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfBusiness_98458a0d-287d-4db9-b457-e53d2bec0023" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GainLossOnSaleOfBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_1002bc87-1c16-4f76-a628-7a1ec23a89a0" xlink:to="loc_us-gaap_GainLossOnSaleOfBusiness_98458a0d-287d-4db9-b457-e53d2bec0023" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InsuredEventGainLoss_d7b4be7d-cc37-4f93-8388-10caf5a39666" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InsuredEventGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_1002bc87-1c16-4f76-a628-7a1ec23a89a0" xlink:to="loc_us-gaap_InsuredEventGainLoss_d7b4be7d-cc37-4f93-8388-10caf5a39666" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_6b74b180-8106-41c3-94e7-920d9d977e5e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentExpenditureAdditionToLongLivedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_1002bc87-1c16-4f76-a628-7a1ec23a89a0" xlink:to="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_6b74b180-8106-41c3-94e7-920d9d977e5e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_bb5e4898-5ca6-4e71-8bbc-48362c12567b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_1002bc87-1c16-4f76-a628-7a1ec23a89a0" xlink:to="loc_us-gaap_Assets_bb5e4898-5ca6-4e71-8bbc-48362c12567b" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.muellerindustries.com/role/FinancialInstrumentsNarrativeDetails" xlink:type="simple" xlink:href="mli-20250628.xsd#FinancialInstrumentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.muellerindustries.com/role/FinancialInstrumentsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_2454de47-8d9d-4d6f-81a7-128e2390ed20" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_59d96234-d922-44a6-b53b-1ac7b7ff1242" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_2454de47-8d9d-4d6f-81a7-128e2390ed20" xlink:to="loc_us-gaap_DerivativeTable_59d96234-d922-44a6-b53b-1ac7b7ff1242" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_3e644702-0791-4a51-af2f-f1a3f87bfc9f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_59d96234-d922-44a6-b53b-1ac7b7ff1242" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_3e644702-0791-4a51-af2f-f1a3f87bfc9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_3e644702-0791-4a51-af2f-f1a3f87bfc9f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_3e644702-0791-4a51-af2f-f1a3f87bfc9f" xlink:to="loc_us-gaap_HedgingRelationshipDomain_3e644702-0791-4a51-af2f-f1a3f87bfc9f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_32b04c8c-abcc-4ca4-9262-932b0e2d566a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_3e644702-0791-4a51-af2f-f1a3f87bfc9f" xlink:to="loc_us-gaap_HedgingRelationshipDomain_32b04c8c-abcc-4ca4-9262-932b0e2d566a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_cca6889b-5b3b-4cb5-b0fa-c6bbeb03c1a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_32b04c8c-abcc-4ca4-9262-932b0e2d566a" xlink:to="loc_us-gaap_CashFlowHedgingMember_cca6889b-5b3b-4cb5-b0fa-c6bbeb03c1a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueHedgingMember_16b6eeb1-4ed6-4a56-9e17-aa5517b2e2f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_32b04c8c-abcc-4ca4-9262-932b0e2d566a" xlink:to="loc_us-gaap_FairValueHedgingMember_16b6eeb1-4ed6-4a56-9e17-aa5517b2e2f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_1c1b0a9e-9020-412a-a5d8-ca4e0fef4a0e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_59d96234-d922-44a6-b53b-1ac7b7ff1242" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_1c1b0a9e-9020-412a-a5d8-ca4e0fef4a0e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_1c1b0a9e-9020-412a-a5d8-ca4e0fef4a0e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_1c1b0a9e-9020-412a-a5d8-ca4e0fef4a0e" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_1c1b0a9e-9020-412a-a5d8-ca4e0fef4a0e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_bb6946bf-e350-4b0b-80d0-9b03a850ea5f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_1c1b0a9e-9020-412a-a5d8-ca4e0fef4a0e" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_bb6946bf-e350-4b0b-80d0-9b03a850ea5f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommodityContractMember_fe67eee2-ed31-4564-9f9d-aad91f6326bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommodityContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_bb6946bf-e350-4b0b-80d0-9b03a850ea5f" xlink:to="loc_us-gaap_CommodityContractMember_fe67eee2-ed31-4564-9f9d-aad91f6326bd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PositionAxis_518261d1-6921-4067-91c7-8231583adb34" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PositionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_59d96234-d922-44a6-b53b-1ac7b7ff1242" xlink:to="loc_us-gaap_PositionAxis_518261d1-6921-4067-91c7-8231583adb34" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PositionDomain_518261d1-6921-4067-91c7-8231583adb34_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PositionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PositionAxis_518261d1-6921-4067-91c7-8231583adb34" xlink:to="loc_us-gaap_PositionDomain_518261d1-6921-4067-91c7-8231583adb34_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PositionDomain_b85296c3-90a1-47dc-a0de-d561528ab98d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PositionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PositionAxis_518261d1-6921-4067-91c7-8231583adb34" xlink:to="loc_us-gaap_PositionDomain_b85296c3-90a1-47dc-a0de-d561528ab98d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongMember_acd08cc0-70fa-4ed8-9ad7-c024883095d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PositionDomain_b85296c3-90a1-47dc-a0de-d561528ab98d" xlink:to="loc_us-gaap_LongMember_acd08cc0-70fa-4ed8-9ad7-c024883095d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortMember_d95b7e5b-5844-4cb8-9082-f07987e43e65" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PositionDomain_b85296c3-90a1-47dc-a0de-d561528ab98d" xlink:to="loc_us-gaap_ShortMember_d95b7e5b-5844-4cb8-9082-f07987e43e65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeNet_a19e7975-0a30-4234-a928-b0df5389313c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeFairValueOfDerivativeNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_2454de47-8d9d-4d6f-81a7-128e2390ed20" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeNet_a19e7975-0a30-4234-a928-b0df5389313c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_TimePeriodForOpenCopperFutureContract_4671170f-d100-44fe-aea0-3779798a9bf2" xlink:href="mli-20250628.xsd#mli_TimePeriodForOpenCopperFutureContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_2454de47-8d9d-4d6f-81a7-128e2390ed20" xlink:to="loc_mli_TimePeriodForOpenCopperFutureContract_4671170f-d100-44fe-aea0-3779798a9bf2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_GainLossOnFairValueOfFutureContracts_8ca8a45c-1d6d-49e3-9e94-70774a615a2c" xlink:href="mli-20250628.xsd#mli_GainLossOnFairValueOfFutureContracts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_2454de47-8d9d-4d6f-81a7-128e2390ed20" xlink:to="loc_mli_GainLossOnFairValueOfFutureContracts_8ca8a45c-1d6d-49e3-9e94-70774a615a2c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromDerivativeInstrumentsEffectNetOfTax_ccc84210-7e7f-4542-b059-d1fd32ce1033" xlink:href="mli-20250628.xsd#mli_AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromDerivativeInstrumentsEffectNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_2454de47-8d9d-4d6f-81a7-128e2390ed20" xlink:to="loc_mli_AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromDerivativeInstrumentsEffectNetOfTax_ccc84210-7e7f-4542-b059-d1fd32ce1033" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_OpenOptionContractsPutAtFairValue_486563ed-ed24-43f3-a142-c4cea0a2ea95" xlink:href="mli-20250628.xsd#mli_OpenOptionContractsPutAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_2454de47-8d9d-4d6f-81a7-128e2390ed20" xlink:to="loc_mli_OpenOptionContractsPutAtFairValue_486563ed-ed24-43f3-a142-c4cea0a2ea95" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_TimePeriodForOpenCopperFutureContractSales_17639690-2c71-440c-ac5a-e32d1cc35ddf" xlink:href="mli-20250628.xsd#mli_TimePeriodForOpenCopperFutureContractSales"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_2454de47-8d9d-4d6f-81a7-128e2390ed20" xlink:to="loc_mli_TimePeriodForOpenCopperFutureContractSales_17639690-2c71-440c-ac5a-e32d1cc35ddf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeCollateralObligationToReturnCash_4edfb636-0604-4f81-a4ec-2b4f260ba326" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeCollateralObligationToReturnCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_2454de47-8d9d-4d6f-81a7-128e2390ed20" xlink:to="loc_us-gaap_DerivativeCollateralObligationToReturnCash_4edfb636-0604-4f81-a4ec-2b4f260ba326" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.muellerindustries.com/role/FinancialInstrumentsScheduleofDerivativeInstrumentsDesignatedasCashFlowHedgesReflectedintheFinancialStatementsDetails" xlink:type="simple" xlink:href="mli-20250628.xsd#FinancialInstrumentsScheduleofDerivativeInstrumentsDesignatedasCashFlowHedgesReflectedintheFinancialStatementsDetails"/>
  <link:definitionLink xlink:role="http://www.muellerindustries.com/role/FinancialInstrumentsScheduleofDerivativeInstrumentsDesignatedasCashFlowHedgesReflectedintheFinancialStatementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativesFairValueLineItems_850ec51f-50e9-4df3-bb8e-8fceb8387bf9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativesFairValueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_bb8b70f5-fb4e-4ee3-ade1-1674bd082c2b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_850ec51f-50e9-4df3-bb8e-8fceb8387bf9" xlink:to="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_bb8b70f5-fb4e-4ee3-ade1-1674bd082c2b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_5b542dc8-e453-45a1-a75e-c282b4a6396e" 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_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_bb8b70f5-fb4e-4ee3-ade1-1674bd082c2b" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_5b542dc8-e453-45a1-a75e-c282b4a6396e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_5b542dc8-e453-45a1-a75e-c282b4a6396e_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_5b542dc8-e453-45a1-a75e-c282b4a6396e" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_5b542dc8-e453-45a1-a75e-c282b4a6396e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_a59f201c-aa85-42ec-9208-8d9e9e3bf6f1" 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_5b542dc8-e453-45a1-a75e-c282b4a6396e" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_a59f201c-aa85-42ec-9208-8d9e9e3bf6f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCurrentAssetsMember_8b16b143-2bc5-4b8a-a857-acaf938723a8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCurrentAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_a59f201c-aa85-42ec-9208-8d9e9e3bf6f1" xlink:to="loc_us-gaap_OtherCurrentAssetsMember_8b16b143-2bc5-4b8a-a857-acaf938723a8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCurrentLiabilitiesMember_565b35e8-8175-42c9-96b5-0b1288f19236" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCurrentLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_a59f201c-aa85-42ec-9208-8d9e9e3bf6f1" xlink:to="loc_us-gaap_OtherCurrentLiabilitiesMember_565b35e8-8175-42c9-96b5-0b1288f19236" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_6fb13c69-0e9a-4378-aebb-82eb974444bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_bb8b70f5-fb4e-4ee3-ade1-1674bd082c2b" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_6fb13c69-0e9a-4378-aebb-82eb974444bd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_6fb13c69-0e9a-4378-aebb-82eb974444bd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_6fb13c69-0e9a-4378-aebb-82eb974444bd" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_6fb13c69-0e9a-4378-aebb-82eb974444bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_b0178d98-08be-4016-aaef-4d181f75cf3f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_6fb13c69-0e9a-4378-aebb-82eb974444bd" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_b0178d98-08be-4016-aaef-4d181f75cf3f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommodityContractMember_338bfdb0-4be4-4d93-a5ed-15580176220d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommodityContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_b0178d98-08be-4016-aaef-4d181f75cf3f" xlink:to="loc_us-gaap_CommodityContractMember_338bfdb0-4be4-4d93-a5ed-15580176220d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_d5d103ed-d6ab-40b5-aea2-cc93825e6a8b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_bb8b70f5-fb4e-4ee3-ade1-1674bd082c2b" xlink:to="loc_us-gaap_HedgingDesignationAxis_d5d103ed-d6ab-40b5-aea2-cc93825e6a8b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_d5d103ed-d6ab-40b5-aea2-cc93825e6a8b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_d5d103ed-d6ab-40b5-aea2-cc93825e6a8b" xlink:to="loc_us-gaap_HedgingDesignationDomain_d5d103ed-d6ab-40b5-aea2-cc93825e6a8b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_7d225ad0-6c4d-4ca0-98f8-d0bd4c82c7d4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_d5d103ed-d6ab-40b5-aea2-cc93825e6a8b" xlink:to="loc_us-gaap_HedgingDesignationDomain_7d225ad0-6c4d-4ca0-98f8-d0bd4c82c7d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_0a135cae-537b-4854-be24-10669dc96b8d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_7d225ad0-6c4d-4ca0-98f8-d0bd4c82c7d4" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_0a135cae-537b-4854-be24-10669dc96b8d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_e5fd23ef-cf5f-4481-8323-5b994214d4ba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_850ec51f-50e9-4df3-bb8e-8fceb8387bf9" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_e5fd23ef-cf5f-4481-8323-5b994214d4ba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetFairValueGrossLiability_215bcd31-5ab5-41ee-9425-02eb779573d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAssetFairValueGrossLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_850ec51f-50e9-4df3-bb8e-8fceb8387bf9" xlink:to="loc_us-gaap_DerivativeAssetFairValueGrossLiability_215bcd31-5ab5-41ee-9425-02eb779573d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_2ee19f93-b35b-4bca-80f5-08f8b1086bae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_850ec51f-50e9-4df3-bb8e-8fceb8387bf9" xlink:to="loc_us-gaap_DerivativeAssets_2ee19f93-b35b-4bca-80f5-08f8b1086bae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilityFairValueGrossAsset_f557c18d-ec9c-4847-9854-aa16064f7a77" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilityFairValueGrossAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_850ec51f-50e9-4df3-bb8e-8fceb8387bf9" xlink:to="loc_us-gaap_DerivativeLiabilityFairValueGrossAsset_f557c18d-ec9c-4847-9854-aa16064f7a77" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_1cf30b8d-69e8-4dd4-b3ac-5075a8af35d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeFairValueOfDerivativeLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_850ec51f-50e9-4df3-bb8e-8fceb8387bf9" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_1cf30b8d-69e8-4dd4-b3ac-5075a8af35d2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_0a0ae23c-a86b-44fc-9c9f-1208ffdcad02" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_850ec51f-50e9-4df3-bb8e-8fceb8387bf9" xlink:to="loc_us-gaap_DerivativeLiabilities_0a0ae23c-a86b-44fc-9c9f-1208ffdcad02" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.muellerindustries.com/role/FinancialInstrumentsScheduleofFairValueHedgesDetails" xlink:type="simple" xlink:href="mli-20250628.xsd#FinancialInstrumentsScheduleofFairValueHedgesDetails"/>
  <link:definitionLink xlink:role="http://www.muellerindustries.com/role/FinancialInstrumentsScheduleofFairValueHedgesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_9c07fefc-18da-4b95-8f9c-ea907fc16648" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_f31f8e5a-6dd1-4031-9707-7ef7c48ea08c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_9c07fefc-18da-4b95-8f9c-ea907fc16648" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_f31f8e5a-6dd1-4031-9707-7ef7c48ea08c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_da004400-caaa-4626-8c4e-66a2bab939e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_f31f8e5a-6dd1-4031-9707-7ef7c48ea08c" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_da004400-caaa-4626-8c4e-66a2bab939e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_da004400-caaa-4626-8c4e-66a2bab939e3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_da004400-caaa-4626-8c4e-66a2bab939e3" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_da004400-caaa-4626-8c4e-66a2bab939e3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_a65f47f0-35e5-4029-80a0-e65178df37bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_da004400-caaa-4626-8c4e-66a2bab939e3" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_a65f47f0-35e5-4029-80a0-e65178df37bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommodityContractMember_addd3a8a-a0ad-4811-b470-c2d699c0f10e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommodityContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_a65f47f0-35e5-4029-80a0-e65178df37bc" xlink:to="loc_us-gaap_CommodityContractMember_addd3a8a-a0ad-4811-b470-c2d699c0f10e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_0c4fd37b-3b9c-401f-b068-73621aab906a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_f31f8e5a-6dd1-4031-9707-7ef7c48ea08c" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_0c4fd37b-3b9c-401f-b068-73621aab906a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_0c4fd37b-3b9c-401f-b068-73621aab906a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_0c4fd37b-3b9c-401f-b068-73621aab906a" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_0c4fd37b-3b9c-401f-b068-73621aab906a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_f7cae6cd-53de-4a2e-b01e-c48c5659b543" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_0c4fd37b-3b9c-401f-b068-73621aab906a" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_f7cae6cd-53de-4a2e-b01e-c48c5659b543" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_85b0d15a-4344-4720-a14f-267e32897322" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_f7cae6cd-53de-4a2e-b01e-c48c5659b543" xlink:to="loc_us-gaap_CostOfSalesMember_85b0d15a-4344-4720-a14f-267e32897322" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_afc9ec07-6422-4e13-b7ff-945e5da9f183" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_f31f8e5a-6dd1-4031-9707-7ef7c48ea08c" xlink:to="loc_us-gaap_HedgingDesignationAxis_afc9ec07-6422-4e13-b7ff-945e5da9f183" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_afc9ec07-6422-4e13-b7ff-945e5da9f183_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_afc9ec07-6422-4e13-b7ff-945e5da9f183" xlink:to="loc_us-gaap_HedgingDesignationDomain_afc9ec07-6422-4e13-b7ff-945e5da9f183_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_904f6184-b810-49c5-b5b8-f7e5ab1916c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_afc9ec07-6422-4e13-b7ff-945e5da9f183" xlink:to="loc_us-gaap_HedgingDesignationDomain_904f6184-b810-49c5-b5b8-f7e5ab1916c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_20d2456b-6808-4f81-a216-79c0e9b735d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_904f6184-b810-49c5-b5b8-f7e5ab1916c2" xlink:to="loc_us-gaap_NondesignatedMember_20d2456b-6808-4f81-a216-79c0e9b735d2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_eb39793d-34de-4dbe-8c8d-eca846257051" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_9c07fefc-18da-4b95-8f9c-ea907fc16648" xlink:to="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_eb39793d-34de-4dbe-8c8d-eca846257051" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.muellerindustries.com/role/FinancialInstrumentsScheduleofActivitiesRelatedtoDerivativeInstrumentsClassifiedasCashFlowHedgesDetails" xlink:type="simple" xlink:href="mli-20250628.xsd#FinancialInstrumentsScheduleofActivitiesRelatedtoDerivativeInstrumentsClassifiedasCashFlowHedgesDetails"/>
  <link:definitionLink xlink:role="http://www.muellerindustries.com/role/FinancialInstrumentsScheduleofActivitiesRelatedtoDerivativeInstrumentsClassifiedasCashFlowHedgesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_71bca4e6-c610-4805-a76e-be37431209d1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01d7395c-a3ab-4a99-acbf-0df59fe2f9b3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_71bca4e6-c610-4805-a76e-be37431209d1" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01d7395c-a3ab-4a99-acbf-0df59fe2f9b3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_ee30f5cc-f67c-48d3-8080-4da29249c7e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01d7395c-a3ab-4a99-acbf-0df59fe2f9b3" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_ee30f5cc-f67c-48d3-8080-4da29249c7e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_ee30f5cc-f67c-48d3-8080-4da29249c7e1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_ee30f5cc-f67c-48d3-8080-4da29249c7e1" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_ee30f5cc-f67c-48d3-8080-4da29249c7e1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_13fcb068-dfd3-4165-857b-1bb2b34bd0a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_ee30f5cc-f67c-48d3-8080-4da29249c7e1" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_13fcb068-dfd3-4165-857b-1bb2b34bd0a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommodityContractMember_e111481c-8f17-42ba-8884-cbb03012a4bf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommodityContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_13fcb068-dfd3-4165-857b-1bb2b34bd0a7" xlink:to="loc_us-gaap_CommodityContractMember_e111481c-8f17-42ba-8884-cbb03012a4bf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherContractMember_1a71458c-6ad9-4782-8bab-9bfafe2a1c2d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_13fcb068-dfd3-4165-857b-1bb2b34bd0a7" xlink:to="loc_us-gaap_OtherContractMember_1a71458c-6ad9-4782-8bab-9bfafe2a1c2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_c77f7534-90fc-421e-818a-0c2d7bfed638" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01d7395c-a3ab-4a99-acbf-0df59fe2f9b3" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_c77f7534-90fc-421e-818a-0c2d7bfed638" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_c77f7534-90fc-421e-818a-0c2d7bfed638_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_c77f7534-90fc-421e-818a-0c2d7bfed638" xlink:to="loc_us-gaap_HedgingRelationshipDomain_c77f7534-90fc-421e-818a-0c2d7bfed638_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_81606574-17b6-423d-b161-28258796d254" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_c77f7534-90fc-421e-818a-0c2d7bfed638" xlink:to="loc_us-gaap_HedgingRelationshipDomain_81606574-17b6-423d-b161-28258796d254" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_5e637729-a22b-48b1-8257-995eef375c10" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_81606574-17b6-423d-b161-28258796d254" xlink:to="loc_us-gaap_CashFlowHedgingMember_5e637729-a22b-48b1-8257-995eef375c10" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_710125e1-45f8-46bd-be6e-201c245b6c11" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01d7395c-a3ab-4a99-acbf-0df59fe2f9b3" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_710125e1-45f8-46bd-be6e-201c245b6c11" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_710125e1-45f8-46bd-be6e-201c245b6c11_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_710125e1-45f8-46bd-be6e-201c245b6c11" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_710125e1-45f8-46bd-be6e-201c245b6c11_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_8812800c-f485-474d-aefc-81f72bc6c17b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_710125e1-45f8-46bd-be6e-201c245b6c11" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_8812800c-f485-474d-aefc-81f72bc6c17b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_80499a72-d7b6-4665-a702-2ab8412cb7e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_8812800c-f485-474d-aefc-81f72bc6c17b" xlink:to="loc_us-gaap_CostOfSalesMember_80499a72-d7b6-4665-a702-2ab8412cb7e7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_de9f59b1-0890-4255-9f76-cce0fb2a1a3f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_71bca4e6-c610-4805-a76e-be37431209d1" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_de9f59b1-0890-4255-9f76-cce0fb2a1a3f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_e898da3e-8937-4874-a6bc-7b89b1af37a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_71bca4e6-c610-4805-a76e-be37431209d1" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_e898da3e-8937-4874-a6bc-7b89b1af37a7" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.muellerindustries.com/role/InvestmentsinUnconsolidatedAffiliatesNarrativeDetails" xlink:type="simple" xlink:href="mli-20250628.xsd#InvestmentsinUnconsolidatedAffiliatesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.muellerindustries.com/role/InvestmentsinUnconsolidatedAffiliatesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_4ab37909-e54a-4747-9718-5c73aa4e6cb2" 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_b97057f5-d573-406e-80cb-a50130e44677" 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_4ab37909-e54a-4747-9718-5c73aa4e6cb2" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_b97057f5-d573-406e-80cb-a50130e44677" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_c204944a-fc19-4724-b73b-7d4e2454c64f" 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_b97057f5-d573-406e-80cb-a50130e44677" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_c204944a-fc19-4724-b73b-7d4e2454c64f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_c204944a-fc19-4724-b73b-7d4e2454c64f_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_c204944a-fc19-4724-b73b-7d4e2454c64f" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_c204944a-fc19-4724-b73b-7d4e2454c64f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_b2c3e49f-c80b-4c52-8779-1e3530160791" 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_c204944a-fc19-4724-b73b-7d4e2454c64f" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_b2c3e49f-c80b-4c52-8779-1e3530160791" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_TecumsehProductsHoldingsLLCMember_0df9718c-3a2f-4a23-8f0b-68ad89efb993" xlink:href="mli-20250628.xsd#mli_TecumsehProductsHoldingsLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_b2c3e49f-c80b-4c52-8779-1e3530160791" xlink:to="loc_mli_TecumsehProductsHoldingsLLCMember_0df9718c-3a2f-4a23-8f0b-68ad89efb993" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_RetailDistributionBusinessMember_c9a9a863-b30d-4abe-8dcb-355db2d744d9" xlink:href="mli-20250628.xsd#mli_RetailDistributionBusinessMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_b2c3e49f-c80b-4c52-8779-1e3530160791" xlink:to="loc_mli_RetailDistributionBusinessMember_c9a9a863-b30d-4abe-8dcb-355db2d744d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_860b8a4e-928e-48d5-be77-3bb48b857839" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_b97057f5-d573-406e-80cb-a50130e44677" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_860b8a4e-928e-48d5-be77-3bb48b857839" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_860b8a4e-928e-48d5-be77-3bb48b857839_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_860b8a4e-928e-48d5-be77-3bb48b857839" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_860b8a4e-928e-48d5-be77-3bb48b857839_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_dae90977-9f36-47dc-b25f-113be397a044" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_860b8a4e-928e-48d5-be77-3bb48b857839" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_dae90977-9f36-47dc-b25f-113be397a044" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_TecumsehProductsHoldingsLLCMember_f6f57e0d-a6a1-49da-8b28-4fa8606eaf23" xlink:href="mli-20250628.xsd#mli_TecumsehProductsHoldingsLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_dae90977-9f36-47dc-b25f-113be397a044" xlink:to="loc_mli_TecumsehProductsHoldingsLLCMember_f6f57e0d-a6a1-49da-8b28-4fa8606eaf23" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_dc429796-659e-46f6-a3ea-73fdca78a048" 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_ScheduleOfEquityMethodInvestmentsTable_b97057f5-d573-406e-80cb-a50130e44677" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_dc429796-659e-46f6-a3ea-73fdca78a048" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_dc429796-659e-46f6-a3ea-73fdca78a048_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_dc429796-659e-46f6-a3ea-73fdca78a048" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_dc429796-659e-46f6-a3ea-73fdca78a048_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e14321c5-446d-4f8c-9915-d82b73b889da" 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_dc429796-659e-46f6-a3ea-73fdca78a048" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e14321c5-446d-4f8c-9915-d82b73b889da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_RetailDistributionBusinessMember_1d58c0fc-6c24-4a4a-bd6a-2e5df15c8640" xlink:href="mli-20250628.xsd#mli_RetailDistributionBusinessMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e14321c5-446d-4f8c-9915-d82b73b889da" xlink:to="loc_mli_RetailDistributionBusinessMember_1d58c0fc-6c24-4a4a-bd6a-2e5df15c8640" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_ed7a34c3-d7d0-492b-a7fb-5861de5336e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_b97057f5-d573-406e-80cb-a50130e44677" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_ed7a34c3-d7d0-492b-a7fb-5861de5336e9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_ed7a34c3-d7d0-492b-a7fb-5861de5336e9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_ed7a34c3-d7d0-492b-a7fb-5861de5336e9" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_ed7a34c3-d7d0-492b-a7fb-5861de5336e9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_0b875d46-0fa3-47c2-acb5-ae3ede25a067" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_ed7a34c3-d7d0-492b-a7fb-5861de5336e9" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_0b875d46-0fa3-47c2-acb5-ae3ede25a067" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_CapitalContributionMember_e32728b6-5b0b-4cc5-8adf-f29028e350cd" xlink:href="mli-20250628.xsd#mli_CapitalContributionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_0b875d46-0fa3-47c2-acb5-ae3ede25a067" xlink:to="loc_mli_CapitalContributionMember_e32728b6-5b0b-4cc5-8adf-f29028e350cd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableMember_deca3536-d53b-4dda-bc9f-9426c49e2048" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NotesReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_0b875d46-0fa3-47c2-acb5-ae3ede25a067" xlink:to="loc_us-gaap_NotesReceivableMember_deca3536-d53b-4dda-bc9f-9426c49e2048" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_841d6c46-75c8-4525-86e3-00159b0ee15d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_4ab37909-e54a-4747-9718-5c73aa4e6cb2" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_841d6c46-75c8-4525-86e3-00159b0ee15d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_5dba8504-57aa-4c30-8ffb-c6d9b93adc7e" 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_ScheduleOfEquityMethodInvestmentsLineItems_4ab37909-e54a-4747-9718-5c73aa4e6cb2" xlink:to="loc_us-gaap_ProfitLoss_5dba8504-57aa-4c30-8ffb-c6d9b93adc7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForAdvanceToAffiliate_777196e9-e090-424e-8cfa-f92d74d30211" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsForAdvanceToAffiliate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_4ab37909-e54a-4747-9718-5c73aa4e6cb2" xlink:to="loc_us-gaap_PaymentsForAdvanceToAffiliate_777196e9-e090-424e-8cfa-f92d74d30211" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.muellerindustries.com/role/BenefitPlansScheduleofComponentsofNetPeriodicBenefitCostIncomeDetails" xlink:type="simple" xlink:href="mli-20250628.xsd#BenefitPlansScheduleofComponentsofNetPeriodicBenefitCostIncomeDetails"/>
  <link:definitionLink xlink:role="http://www.muellerindustries.com/role/BenefitPlansScheduleofComponentsofNetPeriodicBenefitCostIncomeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_4db0c171-954c-4f08-b2bc-097da9fabf6b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable_7df9adff-9bb8-49a1-ab09-5e5311cdb22c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_4db0c171-954c-4f08-b2bc-097da9fabf6b" xlink:to="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable_7df9adff-9bb8-49a1-ab09-5e5311cdb22c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_3ad8ec06-a196-4489-b0b4-7b654219f6b2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable_7df9adff-9bb8-49a1-ab09-5e5311cdb22c" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_3ad8ec06-a196-4489-b0b4-7b654219f6b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_3ad8ec06-a196-4489-b0b4-7b654219f6b2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_3ad8ec06-a196-4489-b0b4-7b654219f6b2" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_3ad8ec06-a196-4489-b0b4-7b654219f6b2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_cd08f75e-a1a9-4100-a433-89ed2cfee8c3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_3ad8ec06-a196-4489-b0b4-7b654219f6b2" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_cd08f75e-a1a9-4100-a433-89ed2cfee8c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_e8996d1c-c73c-4b5a-9cae-faca94f4cde4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_cd08f75e-a1a9-4100-a433-89ed2cfee8c3" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_e8996d1c-c73c-4b5a-9cae-faca94f4cde4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_02e253e8-de23-4794-a3e6-27212a71618b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_cd08f75e-a1a9-4100-a433-89ed2cfee8c3" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_02e253e8-de23-4794-a3e6-27212a71618b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresAbstract_599aa09f-448c-4c87-a4f8-ee9b81965750" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_4db0c171-954c-4f08-b2bc-097da9fabf6b" xlink:to="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresAbstract_599aa09f-448c-4c87-a4f8-ee9b81965750" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanServiceCost_d2fa9135-51ec-4fb1-be2e-bb1455c43b7d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanServiceCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresAbstract_599aa09f-448c-4c87-a4f8-ee9b81965750" xlink:to="loc_us-gaap_DefinedBenefitPlanServiceCost_d2fa9135-51ec-4fb1-be2e-bb1455c43b7d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanInterestCost_d8d675b0-7b4e-4d89-9085-95390543498c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanInterestCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresAbstract_599aa09f-448c-4c87-a4f8-ee9b81965750" xlink:to="loc_us-gaap_DefinedBenefitPlanInterestCost_d8d675b0-7b4e-4d89-9085-95390543498c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_f79e111d-840a-443c-9ee3-58e61adb5028" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresAbstract_599aa09f-448c-4c87-a4f8-ee9b81965750" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_f79e111d-840a-443c-9ee3-58e61adb5028" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_6a92974c-88e6-4200-9849-bb9a8de63644" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresAbstract_599aa09f-448c-4c87-a4f8-ee9b81965750" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_6a92974c-88e6-4200-9849-bb9a8de63644" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_796b2a00-038a-4d22-8479-7aac12d8195d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresAbstract_599aa09f-448c-4c87-a4f8-ee9b81965750" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_796b2a00-038a-4d22-8479-7aac12d8195d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_21253097-1ced-4b0d-8adb-0a479e932478" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresAbstract_599aa09f-448c-4c87-a4f8-ee9b81965750" xlink:to="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_21253097-1ced-4b0d-8adb-0a479e932478" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.muellerindustries.com/role/CommitmentsandContingenciesDetails" xlink:type="simple" xlink:href="mli-20250628.xsd#CommitmentsandContingenciesDetails"/>
  <link:definitionLink xlink:role="http://www.muellerindustries.com/role/CommitmentsandContingenciesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" 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_a461aa30-06d3-464d-8d20-8fa51dc9268a" 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_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_us-gaap_LossContingenciesTable_a461aa30-06d3-464d-8d20-8fa51dc9268a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EnvironmentalRemediationSiteAxis_b80b216d-0393-4955-bed5-9a2fa697fbc3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EnvironmentalRemediationSiteAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_a461aa30-06d3-464d-8d20-8fa51dc9268a" xlink:to="loc_us-gaap_EnvironmentalRemediationSiteAxis_b80b216d-0393-4955-bed5-9a2fa697fbc3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EnvironmentalRemediationSiteDomain_b80b216d-0393-4955-bed5-9a2fa697fbc3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EnvironmentalRemediationSiteDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_EnvironmentalRemediationSiteAxis_b80b216d-0393-4955-bed5-9a2fa697fbc3" xlink:to="loc_us-gaap_EnvironmentalRemediationSiteDomain_b80b216d-0393-4955-bed5-9a2fa697fbc3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EnvironmentalRemediationSiteDomain_020fbbf0-9711-4f72-b00f-4d28333ac40c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EnvironmentalRemediationSiteDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_EnvironmentalRemediationSiteAxis_b80b216d-0393-4955-bed5-9a2fa697fbc3" xlink:to="loc_us-gaap_EnvironmentalRemediationSiteDomain_020fbbf0-9711-4f72-b00f-4d28333ac40c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_SoutheastKansasSitesMember_68c0d3af-cb50-40d7-ace7-41bccf5ab965" xlink:href="mli-20250628.xsd#mli_SoutheastKansasSitesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EnvironmentalRemediationSiteDomain_020fbbf0-9711-4f72-b00f-4d28333ac40c" xlink:to="loc_mli_SoutheastKansasSitesMember_68c0d3af-cb50-40d7-ace7-41bccf5ab965" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_SoutheastKansasSitesLanyonMember_d1859c88-538c-4a29-a77a-dbb1432b5318" xlink:href="mli-20250628.xsd#mli_SoutheastKansasSitesLanyonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EnvironmentalRemediationSiteDomain_020fbbf0-9711-4f72-b00f-4d28333ac40c" xlink:to="loc_mli_SoutheastKansasSitesLanyonMember_d1859c88-538c-4a29-a77a-dbb1432b5318" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_ShastaAreaMineSitesMember_f8f33796-b057-4bc7-9c7a-ac69ac532b1e" xlink:href="mli-20250628.xsd#mli_ShastaAreaMineSitesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EnvironmentalRemediationSiteDomain_020fbbf0-9711-4f72-b00f-4d28333ac40c" xlink:to="loc_mli_ShastaAreaMineSitesMember_f8f33796-b057-4bc7-9c7a-ac69ac532b1e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_LeadRefinerySiteMember_1f877f15-9fd1-4945-88f1-8602595abd7e" xlink:href="mli-20250628.xsd#mli_LeadRefinerySiteMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EnvironmentalRemediationSiteDomain_020fbbf0-9711-4f72-b00f-4d28333ac40c" xlink:to="loc_mli_LeadRefinerySiteMember_1f877f15-9fd1-4945-88f1-8602595abd7e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_LeadRefineryNPLSiteMember_e3b674c9-b881-4c10-8e46-ea2322e04043" xlink:href="mli-20250628.xsd#mli_LeadRefineryNPLSiteMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EnvironmentalRemediationSiteDomain_020fbbf0-9711-4f72-b00f-4d28333ac40c" xlink:to="loc_mli_LeadRefineryNPLSiteMember_e3b674c9-b881-4c10-8e46-ea2322e04043" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_BonitaPeakMiningDistrictMember_89f20246-c0a6-4d3e-a507-667d5f9d04b0" xlink:href="mli-20250628.xsd#mli_BonitaPeakMiningDistrictMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EnvironmentalRemediationSiteDomain_020fbbf0-9711-4f72-b00f-4d28333ac40c" xlink:to="loc_mli_BonitaPeakMiningDistrictMember_89f20246-c0a6-4d3e-a507-667d5f9d04b0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_MuellerCopperTubeProductsIncMember_18bd94af-5e7a-47ad-965b-c5844c61ac2c" xlink:href="mli-20250628.xsd#mli_MuellerCopperTubeProductsIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EnvironmentalRemediationSiteDomain_020fbbf0-9711-4f72-b00f-4d28333ac40c" xlink:to="loc_mli_MuellerCopperTubeProductsIncMember_18bd94af-5e7a-47ad-965b-c5844c61ac2c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_24ea0388-c7b5-4bc2-9fbe-892f56e393bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_a461aa30-06d3-464d-8d20-8fa51dc9268a" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_24ea0388-c7b5-4bc2-9fbe-892f56e393bd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_24ea0388-c7b5-4bc2-9fbe-892f56e393bd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_24ea0388-c7b5-4bc2-9fbe-892f56e393bd" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_24ea0388-c7b5-4bc2-9fbe-892f56e393bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_aceed525-1e86-4966-9db3-971a1f8c2404" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_24ea0388-c7b5-4bc2-9fbe-892f56e393bd" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_aceed525-1e86-4966-9db3-971a1f8c2404" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_NonOperatingPropertiesMember_1d169002-145b-45f7-8814-3da2c3c6fa4e" xlink:href="mli-20250628.xsd#mli_NonOperatingPropertiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_aceed525-1e86-4966-9db3-971a1f8c2404" xlink:to="loc_mli_NonOperatingPropertiesMember_1d169002-145b-45f7-8814-3da2c3c6fa4e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_OperatingPropertiesMember_80778be4-0973-4deb-9cda-9ff54a63ae8c" xlink:href="mli-20250628.xsd#mli_OperatingPropertiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_aceed525-1e86-4966-9db3-971a1f8c2404" xlink:to="loc_mli_OperatingPropertiesMember_80778be4-0973-4deb-9cda-9ff54a63ae8c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_fcabee14-f95d-4f41-8b79-63c180b30fec" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_a461aa30-06d3-464d-8d20-8fa51dc9268a" xlink:to="loc_srt_RangeAxis_fcabee14-f95d-4f41-8b79-63c180b30fec" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_fcabee14-f95d-4f41-8b79-63c180b30fec_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_fcabee14-f95d-4f41-8b79-63c180b30fec" xlink:to="loc_srt_RangeMember_fcabee14-f95d-4f41-8b79-63c180b30fec_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_4d2c0b3b-b80b-4fd1-956a-d8d9efd6e1ed" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_fcabee14-f95d-4f41-8b79-63c180b30fec" xlink:to="loc_srt_RangeMember_4d2c0b3b-b80b-4fd1-956a-d8d9efd6e1ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_8a6cd1ae-348b-4ce8-8149-96ef72def27e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_4d2c0b3b-b80b-4fd1-956a-d8d9efd6e1ed" xlink:to="loc_srt_MinimumMember_8a6cd1ae-348b-4ce8-8149-96ef72def27e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_8c6293c6-f75b-4d7d-903b-fb75a9f38f0e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_4d2c0b3b-b80b-4fd1-956a-d8d9efd6e1ed" xlink:to="loc_srt_MaximumMember_8c6293c6-f75b-4d7d-903b-fb75a9f38f0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_39a72c74-6b42-4c51-97e5-39c1bb08c8ff" 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_a461aa30-06d3-464d-8d20-8fa51dc9268a" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_39a72c74-6b42-4c51-97e5-39c1bb08c8ff" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_39a72c74-6b42-4c51-97e5-39c1bb08c8ff_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_39a72c74-6b42-4c51-97e5-39c1bb08c8ff" xlink:to="loc_us-gaap_LossContingencyNatureDomain_39a72c74-6b42-4c51-97e5-39c1bb08c8ff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_00b7a81b-0e72-48ee-a886-55ff0bed04a6" 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_39a72c74-6b42-4c51-97e5-39c1bb08c8ff" xlink:to="loc_us-gaap_LossContingencyNatureDomain_00b7a81b-0e72-48ee-a886-55ff0bed04a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnfavorableRegulatoryActionMember_c2679ce8-a373-41d0-a2ad-0421f0e4b4f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnfavorableRegulatoryActionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_00b7a81b-0e72-48ee-a886-55ff0bed04a6" xlink:to="loc_us-gaap_UnfavorableRegulatoryActionMember_c2679ce8-a373-41d0-a2ad-0421f0e4b4f0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_NumberOfFormerSmelterSites_f14156bc-7066-4e86-a6ae-065564810b34" xlink:href="mli-20250628.xsd#mli_NumberOfFormerSmelterSites"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_mli_NumberOfFormerSmelterSites_f14156bc-7066-4e86-a6ae-065564810b34" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccrualForEnvironmentalLossContingenciesGross_f47103b3-9fc7-4172-b0ca-77c55c2ba5e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccrualForEnvironmentalLossContingenciesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_us-gaap_AccrualForEnvironmentalLossContingenciesGross_f47103b3-9fc7-4172-b0ca-77c55c2ba5e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_GeographicBoundaryOfSites_ca76460d-172e-4280-b8c1-eabe07296d69" xlink:href="mli-20250628.xsd#mli_GeographicBoundaryOfSites"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_mli_GeographicBoundaryOfSites_ca76460d-172e-4280-b8c1-eabe07296d69" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_NumberOfPartiesInvolvedInSettlementNegotiations_2561faa2-6a83-489c-88af-80dca2689ce2" xlink:href="mli-20250628.xsd#mli_NumberOfPartiesInvolvedInSettlementNegotiations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_mli_NumberOfPartiesInvolvedInSettlementNegotiations_2561faa2-6a83-489c-88af-80dca2689ce2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_NumberOfPropertiesInRemediation_efd6d878-15c5-4357-b9e7-253d9006ed59" xlink:href="mli-20250628.xsd#mli_NumberOfPropertiesInRemediation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_mli_NumberOfPropertiesInRemediation_efd6d878-15c5-4357-b9e7-253d9006ed59" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_NumberOfSurroundingProperties_af3a3dbf-f4b2-418a-b08c-fa1fef6a2c5c" xlink:href="mli-20250628.xsd#mli_NumberOfSurroundingProperties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_mli_NumberOfSurroundingProperties_af3a3dbf-f4b2-418a-b08c-fa1fef6a2c5c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_PeriodOfPermitImplementationOfBestManagementPractices_f062aa20-3e02-45ed-82a8-014b574c3dfd" xlink:href="mli-20250628.xsd#mli_PeriodOfPermitImplementationOfBestManagementPractices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_mli_PeriodOfPermitImplementationOfBestManagementPractices_f062aa20-3e02-45ed-82a8-014b574c3dfd" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EnvironmentalExitCostsReasonablyPossibleAdditionalLoss_381bc1c0-7d2b-4ef6-836c-e4748caa3948" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EnvironmentalExitCostsReasonablyPossibleAdditionalLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_us-gaap_EnvironmentalExitCostsReasonablyPossibleAdditionalLoss_381bc1c0-7d2b-4ef6-836c-e4748caa3948" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_SiteContingencyEstimatedTimeFrameToResolveContingency1_ae8a8d86-887f-47b9-8434-f86e45d726f3" xlink:href="mli-20250628.xsd#mli_SiteContingencyEstimatedTimeFrameToResolveContingency1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_mli_SiteContingencyEstimatedTimeFrameToResolveContingency1_ae8a8d86-887f-47b9-8434-f86e45d726f3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_SiteContingencyPropertiesLossExposureNotAccruedBestEstimate_03a9da49-0cf5-4e09-a0cf-6a2031517432" xlink:href="mli-20250628.xsd#mli_SiteContingencyPropertiesLossExposureNotAccruedBestEstimate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_mli_SiteContingencyPropertiesLossExposureNotAccruedBestEstimate_03a9da49-0cf5-4e09-a0cf-6a2031517432" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_SiteContingencyEnvironmentalRemedialandFeasibilityStudyFinancialGuarantee_5597f085-44e7-414e-9ae7-08e3493f43e1" xlink:href="mli-20250628.xsd#mli_SiteContingencyEnvironmentalRemedialandFeasibilityStudyFinancialGuarantee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_mli_SiteContingencyEnvironmentalRemedialandFeasibilityStudyFinancialGuarantee_5597f085-44e7-414e-9ae7-08e3493f43e1" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_SiteContingencyNumberOfUnilateralAdministrativeOrders_0f59df26-0812-414a-abb0-347612211679" xlink:href="mli-20250628.xsd#mli_SiteContingencyNumberOfUnilateralAdministrativeOrders"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_mli_SiteContingencyNumberOfUnilateralAdministrativeOrders_0f59df26-0812-414a-abb0-347612211679" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_SiteContingencyNumberOfPotentiallyResponsibleParties_4da19132-5f0b-429d-bece-87297babb9b2" xlink:href="mli-20250628.xsd#mli_SiteContingencyNumberOfPotentiallyResponsibleParties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_mli_SiteContingencyNumberOfPotentiallyResponsibleParties_4da19132-5f0b-429d-bece-87297babb9b2" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccrualForEnvironmentalLossContingencies_f7fbd4b1-576f-4dd0-8acd-dd25aa66c86d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccrualForEnvironmentalLossContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_us-gaap_AccrualForEnvironmentalLossContingencies_f7fbd4b1-576f-4dd0-8acd-dd25aa66c86d" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_SiteContingencyTotalCostForAllPartiesBestEstimate_706ab3f1-00fe-4e5d-8a0d-3293618a674c" xlink:href="mli-20250628.xsd#mli_SiteContingencyTotalCostForAllPartiesBestEstimate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_mli_SiteContingencyTotalCostForAllPartiesBestEstimate_706ab3f1-00fe-4e5d-8a0d-3293618a674c" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_SiteContingencyReimbursementCostsToThirdPartiesForPastCosts_640a778c-8dbb-4988-8f7f-e90a5e0a5884" xlink:href="mli-20250628.xsd#mli_SiteContingencyReimbursementCostsToThirdPartiesForPastCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_mli_SiteContingencyReimbursementCostsToThirdPartiesForPastCosts_640a778c-8dbb-4988-8f7f-e90a5e0a5884" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_SiteContingencyAdditionalReimbursementCostsToThirdPartiesForPastCosts_986378f4-18c5-4e88-ad20-503304685a67" xlink:href="mli-20250628.xsd#mli_SiteContingencyAdditionalReimbursementCostsToThirdPartiesForPastCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_mli_SiteContingencyAdditionalReimbursementCostsToThirdPartiesForPastCosts_986378f4-18c5-4e88-ad20-503304685a67" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyLossInPeriod_755988ae-4301-450d-abfe-61214e0f6d27" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyLossInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_us-gaap_LossContingencyLossInPeriod_755988ae-4301-450d-abfe-61214e0f6d27" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyAccrualAtCarryingValue_75dae0bd-db7b-4047-822c-3715007175af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyAccrualAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_us-gaap_LossContingencyAccrualAtCarryingValue_75dae0bd-db7b-4047-822c-3715007175af" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementAmountAwardedToOtherParty_a3be0177-232b-4505-91b5-947f6523ab44" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LitigationSettlementAmountAwardedToOtherParty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_us-gaap_LitigationSettlementAmountAwardedToOtherParty_a3be0177-232b-4505-91b5-947f6523ab44" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_NumberOfMiningSites_8567ef70-cd32-46d4-9ad1-73ce12838d98" xlink:href="mli-20250628.xsd#mli_NumberOfMiningSites"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_mli_NumberOfMiningSites_8567ef70-cd32-46d4-9ad1-73ce12838d98" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_AssignmentOfAntidumpingDutyRateOnUSImportsByCompanySubsidiaries_5de0df11-8e31-4a36-aa52-60053505f979" xlink:href="mli-20250628.xsd#mli_AssignmentOfAntidumpingDutyRateOnUSImportsByCompanySubsidiaries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_mli_AssignmentOfAntidumpingDutyRateOnUSImportsByCompanySubsidiaries_5de0df11-8e31-4a36-aa52-60053505f979" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_PaymentForInterestAndDuties_e8cd5233-2aaf-4a3f-ae7e-39420f8ad0bf" xlink:href="mli-20250628.xsd#mli_PaymentForInterestAndDuties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_mli_PaymentForInterestAndDuties_e8cd5233-2aaf-4a3f-ae7e-39420f8ad0bf" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_NumberOfImportEntries_cb5e39df-d33c-4d4d-a765-573a982bcf90" xlink:href="mli-20250628.xsd#mli_NumberOfImportEntries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_mli_NumberOfImportEntries_cb5e39df-d33c-4d4d-a765-573a982bcf90" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_TermOfGuarantees_871ad4a6-410f-4f83-b0f5-02339f1305e7" xlink:href="mli-20250628.xsd#mli_TermOfGuarantees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_mli_TermOfGuarantees_871ad4a6-410f-4f83-b0f5-02339f1305e7" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GuaranteeObligationsMaximumExposure_f3409965-2ba0-4167-83e8-7a9c455eedc1" 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_LossContingenciesLineItems_758c8766-657e-4f8e-b930-1a8dd0b1a490" xlink:to="loc_us-gaap_GuaranteeObligationsMaximumExposure_f3409965-2ba0-4167-83e8-7a9c455eedc1" xlink:type="arc" order="25"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.muellerindustries.com/role/AccumulatedOtherComprehensiveIncomeLossScheduleofChangesinAOCIbyComponentNetofTaxesandNoncontrollingInterestDetails" xlink:type="simple" xlink:href="mli-20250628.xsd#AccumulatedOtherComprehensiveIncomeLossScheduleofChangesinAOCIbyComponentNetofTaxesandNoncontrollingInterestDetails"/>
  <link:definitionLink xlink:role="http://www.muellerindustries.com/role/AccumulatedOtherComprehensiveIncomeLossScheduleofChangesinAOCIbyComponentNetofTaxesandNoncontrollingInterestDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_1714ed4a-17cb-4d3e-ad7e-c2ce2de6e106" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_30fc9421-0b25-4aca-b0c5-9702dc6e655f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_1714ed4a-17cb-4d3e-ad7e-c2ce2de6e106" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_30fc9421-0b25-4aca-b0c5-9702dc6e655f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_13cb5fcb-1af3-4ae6-a14f-14bbc76fd73d" 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_AccumulatedOtherComprehensiveIncomeLossTable_30fc9421-0b25-4aca-b0c5-9702dc6e655f" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_13cb5fcb-1af3-4ae6-a14f-14bbc76fd73d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_13cb5fcb-1af3-4ae6-a14f-14bbc76fd73d_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_13cb5fcb-1af3-4ae6-a14f-14bbc76fd73d" xlink:to="loc_us-gaap_EquityComponentDomain_13cb5fcb-1af3-4ae6-a14f-14bbc76fd73d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_20b23051-53be-4af7-852b-5c8be6098889" 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_13cb5fcb-1af3-4ae6-a14f-14bbc76fd73d" xlink:to="loc_us-gaap_EquityComponentDomain_20b23051-53be-4af7-852b-5c8be6098889" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_8f3186ab-520e-41ba-a999-ead67b875f2c" 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_EquityComponentDomain_20b23051-53be-4af7-852b-5c8be6098889" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_8f3186ab-520e-41ba-a999-ead67b875f2c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_f9e075c5-7636-4070-9e4d-01139b43260d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedTranslationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_8f3186ab-520e-41ba-a999-ead67b875f2c" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_f9e075c5-7636-4070-9e4d-01139b43260d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_dee9480e-4485-485a-ba32-8595903b02b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_8f3186ab-520e-41ba-a999-ead67b875f2c" xlink:to="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_dee9480e-4485-485a-ba32-8595903b02b9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_f0905d2a-062a-43e7-99f9-d0d49ee4ef98" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_8f3186ab-520e-41ba-a999-ead67b875f2c" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_f0905d2a-062a-43e7-99f9-d0d49ee4ef98" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_AccumulatedOtherComprehensiveIncomeAttributabletoUnconsolidatedAffiliatesMember_fabb331d-c087-4d40-9c7e-c287e22b0528" xlink:href="mli-20250628.xsd#mli_AccumulatedOtherComprehensiveIncomeAttributabletoUnconsolidatedAffiliatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_8f3186ab-520e-41ba-a999-ead67b875f2c" xlink:to="loc_mli_AccumulatedOtherComprehensiveIncomeAttributabletoUnconsolidatedAffiliatesMember_fabb331d-c087-4d40-9c7e-c287e22b0528" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_7336e446-3276-4904-a1c4-3105edd43a8e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AOCIAttributableToParentNetOfTaxRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_1714ed4a-17cb-4d3e-ad7e-c2ce2de6e106" xlink:to="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_7336e446-3276-4904-a1c4-3105edd43a8e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_a5d4220a-88c1-485f-a9b8-2b38a8376911" 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_AOCIAttributableToParentNetOfTaxRollForward_7336e446-3276-4904-a1c4-3105edd43a8e" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_a5d4220a-88c1-485f-a9b8-2b38a8376911" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_2b4bcd84-f898-44ee-931c-2a1ca2369941" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_7336e446-3276-4904-a1c4-3105edd43a8e" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_2b4bcd84-f898-44ee-931c-2a1ca2369941" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_cd972e9a-426e-41bf-b910-4071bddf0336" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_7336e446-3276-4904-a1c4-3105edd43a8e" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_cd972e9a-426e-41bf-b910-4071bddf0336" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_d429c241-62c2-4815-b4cd-881bf541c234" 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_AOCIAttributableToParentNetOfTaxRollForward_7336e446-3276-4904-a1c4-3105edd43a8e" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_d429c241-62c2-4815-b4cd-881bf541c234" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_a49ae313-0fcb-4f34-a31e-abd83a4d94fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.muellerindustries.com/role/AccumulatedOtherComprehensiveIncomeLossScheduleofReclassificationAdjustmentsOutofAOCIDetails" xlink:type="simple" xlink:href="mli-20250628.xsd#AccumulatedOtherComprehensiveIncomeLossScheduleofReclassificationAdjustmentsOutofAOCIDetails"/>
  <link:definitionLink xlink:role="http://www.muellerindustries.com/role/AccumulatedOtherComprehensiveIncomeLossScheduleofReclassificationAdjustmentsOutofAOCIDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_b816dd1a-2dcb-42e6-b872-4a6da5da8d55" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_f22f785a-9fdb-4471-9943-145a7a6210e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_b816dd1a-2dcb-42e6-b872-4a6da5da8d55" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_f22f785a-9fdb-4471-9943-145a7a6210e4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_dd0b4250-4386-49a7-b918-37110667d7cc" 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_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_f22f785a-9fdb-4471-9943-145a7a6210e4" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_dd0b4250-4386-49a7-b918-37110667d7cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_dd0b4250-4386-49a7-b918-37110667d7cc_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_dd0b4250-4386-49a7-b918-37110667d7cc" xlink:to="loc_us-gaap_EquityComponentDomain_dd0b4250-4386-49a7-b918-37110667d7cc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_65eb2be3-0876-44a4-99b3-c7dbf959b60e" 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_dd0b4250-4386-49a7-b918-37110667d7cc" xlink:to="loc_us-gaap_EquityComponentDomain_65eb2be3-0876-44a4-99b3-c7dbf959b60e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_f90479b7-d6ba-4453-bad5-9c1b0748bf36" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_65eb2be3-0876-44a4-99b3-c7dbf959b60e" xlink:to="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_f90479b7-d6ba-4453-bad5-9c1b0748bf36" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_063ea79c-c0c9-443c-8e45-974c48399f1b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_65eb2be3-0876-44a4-99b3-c7dbf959b60e" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_063ea79c-c0c9-443c-8e45-974c48399f1b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_ec9d5351-cbb9-4e4c-bf56-fdd79509c497" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_f22f785a-9fdb-4471-9943-145a7a6210e4" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_ec9d5351-cbb9-4e4c-bf56-fdd79509c497" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_ec9d5351-cbb9-4e4c-bf56-fdd79509c497_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_ec9d5351-cbb9-4e4c-bf56-fdd79509c497" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_ec9d5351-cbb9-4e4c-bf56-fdd79509c497_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_f0bc3c73-c10f-491e-82c3-eb567056bc5c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_ec9d5351-cbb9-4e4c-bf56-fdd79509c497" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_f0bc3c73-c10f-491e-82c3-eb567056bc5c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_8e66cd06-fe2b-4096-833d-40980d85f841" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_f0bc3c73-c10f-491e-82c3-eb567056bc5c" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_8e66cd06-fe2b-4096-833d-40980d85f841" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_b6a87c1d-cfec-4bda-ad01-3c03e4eb8ca5" 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_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_b816dd1a-2dcb-42e6-b872-4a6da5da8d55" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_b6a87c1d-cfec-4bda-ad01-3c03e4eb8ca5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_6dbc86c6-507d-47e5-9ef3-e86f9842e851" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_b816dd1a-2dcb-42e6-b872-4a6da5da8d55" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_6dbc86c6-507d-47e5-9ef3-e86f9842e851" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_d00785d6-7125-4237-8062-8efdf6e2a804" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_b816dd1a-2dcb-42e6-b872-4a6da5da8d55" xlink:to="loc_us-gaap_NetIncomeLoss_d00785d6-7125-4237-8062-8efdf6e2a804" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_7b009f5c-0275-4734-b6c3-f68593805a31" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_b816dd1a-2dcb-42e6-b872-4a6da5da8d55" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_7b009f5c-0275-4734-b6c3-f68593805a31" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#IndividualsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllIndividualsMember" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#ecd_AllIndividualsMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_mli_JeffreyMartinMember_48c260be-946b-4416-9a88-ac3ffeaa3191" xlink:href="mli-20250628.xsd#mli_JeffreyMartinMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_mli_JeffreyMartinMember_48c260be-946b-4416-9a88-ac3ffeaa3191" xlink:type="arc" order="2"/>
  </link:definitionLink>
</link:linkbase>
