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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2023 Workiva-->
<!--r:0e2bb204-c2b2-499b-b3fa-efe96f44a292,g:c21f5fea-070c-4b9d-a652-99242e7da825-->
<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.aciworldwide.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS" xlink:type="simple" xlink:href="aciw-20230930.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS"/>
  <link:definitionLink xlink:role="http://www.aciworldwide.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_38f399ef-a4a0-413e-8e8f-c738022678cf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_623862fe-0c26-4298-bbc9-b57d1b393551" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_38f399ef-a4a0-413e-8e8f-c738022678cf" xlink:to="loc_us-gaap_RevenuesAbstract_623862fe-0c26-4298-bbc9-b57d1b393551" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_b48cb4dc-cb41-4edf-a872-e1d2d41227b3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_623862fe-0c26-4298-bbc9-b57d1b393551" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_b48cb4dc-cb41-4edf-a872-e1d2d41227b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_d1cd0ac5-a881-4d9d-8d58-fc75d9ac7d8a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_38f399ef-a4a0-413e-8e8f-c738022678cf" xlink:to="loc_us-gaap_OperatingExpensesAbstract_d1cd0ac5-a881-4d9d-8d58-fc75d9ac7d8a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenue_3108992c-aaf4-4202-9219-2cbd138e5e38" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CostOfRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_d1cd0ac5-a881-4d9d-8d58-fc75d9ac7d8a" xlink:to="loc_us-gaap_CostOfRevenue_3108992c-aaf4-4202-9219-2cbd138e5e38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseSoftwareExcludingAcquiredInProcessCost_b3fe5857-aef5-4c8b-8807-4790baad120e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ResearchAndDevelopmentExpenseSoftwareExcludingAcquiredInProcessCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_d1cd0ac5-a881-4d9d-8d58-fc75d9ac7d8a" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseSoftwareExcludingAcquiredInProcessCost_b3fe5857-aef5-4c8b-8807-4790baad120e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpense_57319a3a-23c1-4156-bd99-b6841460c583" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SellingAndMarketingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_d1cd0ac5-a881-4d9d-8d58-fc75d9ac7d8a" xlink:to="loc_us-gaap_SellingAndMarketingExpense_57319a3a-23c1-4156-bd99-b6841460c583" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_860a8d6d-884c-4cb9-ae9e-b36679f64752" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_d1cd0ac5-a881-4d9d-8d58-fc75d9ac7d8a" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_860a8d6d-884c-4cb9-ae9e-b36679f64752" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_c91a0847-563f-4188-b51f-c16837aec078" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_d1cd0ac5-a881-4d9d-8d58-fc75d9ac7d8a" xlink:to="loc_us-gaap_DepreciationAndAmortization_c91a0847-563f-4188-b51f-c16837aec078" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_c254df31-a820-49c4-baa7-8ea147b19a7b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_d1cd0ac5-a881-4d9d-8d58-fc75d9ac7d8a" xlink:to="loc_us-gaap_CostsAndExpenses_c254df31-a820-49c4-baa7-8ea147b19a7b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_497f4f88-9c33-4c43-ab6d-5d65eb3f5017" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_38f399ef-a4a0-413e-8e8f-c738022678cf" xlink:to="loc_us-gaap_OperatingIncomeLoss_497f4f88-9c33-4c43-ab6d-5d65eb3f5017" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpenseAbstract_8dede204-f12d-430e-8648-a9ae44503082" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NonoperatingIncomeExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_38f399ef-a4a0-413e-8e8f-c738022678cf" xlink:to="loc_us-gaap_NonoperatingIncomeExpenseAbstract_8dede204-f12d-430e-8648-a9ae44503082" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_cfa7d7a7-7c60-4efb-b4a5-9b67c854e6c6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_8dede204-f12d-430e-8648-a9ae44503082" xlink:to="loc_us-gaap_InterestExpense_cfa7d7a7-7c60-4efb-b4a5-9b67c854e6c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInterest_01e4ad25-4e37-4ed9-90ef-34a631d03c11" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InvestmentIncomeInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_8dede204-f12d-430e-8648-a9ae44503082" xlink:to="loc_us-gaap_InvestmentIncomeInterest_01e4ad25-4e37-4ed9-90ef-34a631d03c11" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_bd55e418-4ced-401f-bc42-7cdecbf4fd48" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_8dede204-f12d-430e-8648-a9ae44503082" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_bd55e418-4ced-401f-bc42-7cdecbf4fd48" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_9c3cdf41-9bf3-44da-9b32-2874f4224629" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_8dede204-f12d-430e-8648-a9ae44503082" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_9c3cdf41-9bf3-44da-9b32-2874f4224629" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_4e863beb-6c7b-47af-8364-68ebe1867ddb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_38f399ef-a4a0-413e-8e8f-c738022678cf" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_4e863beb-6c7b-47af-8364-68ebe1867ddb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_25968209-1d3c-4c27-bd74-d91cc8f58734" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_38f399ef-a4a0-413e-8e8f-c738022678cf" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_25968209-1d3c-4c27-bd74-d91cc8f58734" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_00d67d2a-3d79-45fd-bb57-bb147894025a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_38f399ef-a4a0-413e-8e8f-c738022678cf" xlink:to="loc_us-gaap_NetIncomeLoss_00d67d2a-3d79-45fd-bb57-bb147894025a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareAbstract_d768971d-d9e3-443d-b70d-6f18582c7aac" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EarningsPerShareAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_38f399ef-a4a0-413e-8e8f-c738022678cf" xlink:to="loc_us-gaap_EarningsPerShareAbstract_d768971d-d9e3-443d-b70d-6f18582c7aac" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_9f33536d-5b74-4707-aca1-27b0993e27b1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_d768971d-d9e3-443d-b70d-6f18582c7aac" xlink:to="loc_us-gaap_EarningsPerShareBasic_9f33536d-5b74-4707-aca1-27b0993e27b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_012213bd-528a-450c-b188-80a8bd14cfd4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_d768971d-d9e3-443d-b70d-6f18582c7aac" xlink:to="loc_us-gaap_EarningsPerShareDiluted_012213bd-528a-450c-b188-80a8bd14cfd4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_6377f15c-2611-419e-9369-b880ce5eed5c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_38f399ef-a4a0-413e-8e8f-c738022678cf" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_6377f15c-2611-419e-9369-b880ce5eed5c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_5ce33505-9d5f-466e-bcc4-e58d1409a586" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_6377f15c-2611-419e-9369-b880ce5eed5c" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_5ce33505-9d5f-466e-bcc4-e58d1409a586" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_752f718b-d940-4693-9e0f-78054f80fca2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_6377f15c-2611-419e-9369-b880ce5eed5c" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_752f718b-d940-4693-9e0f-78054f80fca2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_8ee15802-a87e-44cd-9ef4-818feb9fd25b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_38f399ef-a4a0-413e-8e8f-c738022678cf" xlink:to="loc_us-gaap_StatementTable_8ee15802-a87e-44cd-9ef4-818feb9fd25b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_4fabbed1-f438-455b-b01b-2863b490f8f0" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_8ee15802-a87e-44cd-9ef4-818feb9fd25b" xlink:to="loc_srt_ProductOrServiceAxis_4fabbed1-f438-455b-b01b-2863b490f8f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_4fabbed1-f438-455b-b01b-2863b490f8f0_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_4fabbed1-f438-455b-b01b-2863b490f8f0" xlink:to="loc_srt_ProductsAndServicesDomain_4fabbed1-f438-455b-b01b-2863b490f8f0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_56751a03-f267-4f0f-a370-87ec432ac682" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_4fabbed1-f438-455b-b01b-2863b490f8f0" xlink:to="loc_srt_ProductsAndServicesDomain_56751a03-f267-4f0f-a370-87ec432ac682" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_SoftwareAsServiceAndPlatformAsServiceMember_cb5b96e2-692d-444b-a607-60aca81771ce" xlink:href="aciw-20230930.xsd#aciw_SoftwareAsServiceAndPlatformAsServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_56751a03-f267-4f0f-a370-87ec432ac682" xlink:to="loc_aciw_SoftwareAsServiceAndPlatformAsServiceMember_cb5b96e2-692d-444b-a607-60aca81771ce" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LicenseMember_5ec88b7a-06fa-4eaf-a6d2-97958ed98d62" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_56751a03-f267-4f0f-a370-87ec432ac682" xlink:to="loc_us-gaap_LicenseMember_5ec88b7a-06fa-4eaf-a6d2-97958ed98d62" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaintenanceMember_5ca8face-9815-4d04-b4c3-413e40e15e25" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MaintenanceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_56751a03-f267-4f0f-a370-87ec432ac682" xlink:to="loc_us-gaap_MaintenanceMember_5ca8face-9815-4d04-b4c3-413e40e15e25" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TechnologyServiceMember_efb5b1e2-effc-4b22-9261-8c4c6354136a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TechnologyServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_56751a03-f267-4f0f-a370-87ec432ac682" xlink:to="loc_us-gaap_TechnologyServiceMember_efb5b1e2-effc-4b22-9261-8c4c6354136a" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.aciworldwide.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="simple" xlink:href="aciw-20230930.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY"/>
  <link:definitionLink xlink:role="http://www.aciworldwide.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_8969c8a4-c3cb-40bc-90f2-5044f1875212" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_a9a90eb3-e54b-4d60-87bb-8eee32e25e24" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_8969c8a4-c3cb-40bc-90f2-5044f1875212" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_a9a90eb3-e54b-4d60-87bb-8eee32e25e24" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_151c2548-e984-44b2-a097-f5eeb9d5c0fe" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_a9a90eb3-e54b-4d60-87bb-8eee32e25e24" xlink:to="loc_us-gaap_StockholdersEquity_151c2548-e984-44b2-a097-f5eeb9d5c0fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_4497cb71-4f8a-4130-9f05-438ab28a714c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_a9a90eb3-e54b-4d60-87bb-8eee32e25e24" xlink:to="loc_us-gaap_NetIncomeLoss_4497cb71-4f8a-4130-9f05-438ab28a714c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_23a0a0b1-f362-4ca8-b69e-fa2421b99468" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_a9a90eb3-e54b-4d60-87bb-8eee32e25e24" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_23a0a0b1-f362-4ca8-b69e-fa2421b99468" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_301b3708-b650-445b-aaa5-d54e71f2bfc5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_a9a90eb3-e54b-4d60-87bb-8eee32e25e24" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_301b3708-b650-445b-aaa5-d54e71f2bfc5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_b5551fd3-ebe0-4b8c-8554-67202ae27cbe" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_a9a90eb3-e54b-4d60-87bb-8eee32e25e24" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_b5551fd3-ebe0-4b8c-8554-67202ae27cbe" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_fb04f307-2f5d-417e-a2ea-c1413fc6ab22" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_a9a90eb3-e54b-4d60-87bb-8eee32e25e24" xlink:to="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_fb04f307-2f5d-417e-a2ea-c1413fc6ab22" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_2400e0a5-6406-4971-83b8-d05084e4ba0d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_a9a90eb3-e54b-4d60-87bb-8eee32e25e24" xlink:to="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_2400e0a5-6406-4971-83b8-d05084e4ba0d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_0f10d236-d8c2-4a20-8f8e-00867259ae13" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_12fa4396-a0cc-4f77-aa3c-b0437d4fef17" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_8969c8a4-c3cb-40bc-90f2-5044f1875212" xlink:to="loc_us-gaap_StatementTable_12fa4396-a0cc-4f77-aa3c-b0437d4fef17" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_c022f690-75af-4768-95bf-fc68a76e7f4d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_12fa4396-a0cc-4f77-aa3c-b0437d4fef17" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_c022f690-75af-4768-95bf-fc68a76e7f4d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_c022f690-75af-4768-95bf-fc68a76e7f4d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_c022f690-75af-4768-95bf-fc68a76e7f4d" xlink:to="loc_us-gaap_EquityComponentDomain_c022f690-75af-4768-95bf-fc68a76e7f4d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_d81e32e9-f612-4d1c-b598-d47105b789be" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_c022f690-75af-4768-95bf-fc68a76e7f4d" xlink:to="loc_us-gaap_EquityComponentDomain_d81e32e9-f612-4d1c-b598-d47105b789be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_c40209f4-ca77-4f7c-8e33-de74be43db1d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_d81e32e9-f612-4d1c-b598-d47105b789be" xlink:to="loc_us-gaap_CommonStockMember_c40209f4-ca77-4f7c-8e33-de74be43db1d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_a264aa48-f776-4cbf-852f-9db35c599a37" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_d81e32e9-f612-4d1c-b598-d47105b789be" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_a264aa48-f776-4cbf-852f-9db35c599a37" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_f468f334-a5d6-485c-9c51-34fa83e92754" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_d81e32e9-f612-4d1c-b598-d47105b789be" xlink:to="loc_us-gaap_RetainedEarningsMember_f468f334-a5d6-485c-9c51-34fa83e92754" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_857ea68a-0c45-465d-acd7-755751f88a52" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_d81e32e9-f612-4d1c-b598-d47105b789be" xlink:to="loc_us-gaap_TreasuryStockCommonMember_857ea68a-0c45-465d-acd7-755751f88a52" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_c6bf8bf0-da2f-4c5c-80c1-e3f823460da8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_d81e32e9-f612-4d1c-b598-d47105b789be" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_c6bf8bf0-da2f-4c5c-80c1-e3f823460da8" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.aciworldwide.com/role/StockBasedCompensationPlansTables" xlink:type="simple" xlink:href="aciw-20230930.xsd#StockBasedCompensationPlansTables"/>
  <link:definitionLink xlink:role="http://www.aciworldwide.com/role/StockBasedCompensationPlansTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_54b1ece6-d855-4794-8105-622ba407b1bc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock_656ec3c7-8c37-44ab-be18-60c4c1c69c29" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_54b1ece6-d855-4794-8105-622ba407b1bc" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock_656ec3c7-8c37-44ab-be18-60c4c1c69c29" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfNonvestedPerformanceBasedUnitsActivityTableTextBlock_d7e3bf1d-f524-456f-ba66-c469aae57b94" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfNonvestedPerformanceBasedUnitsActivityTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_54b1ece6-d855-4794-8105-622ba407b1bc" xlink:to="loc_us-gaap_ScheduleOfNonvestedPerformanceBasedUnitsActivityTableTextBlock_d7e3bf1d-f524-456f-ba66-c469aae57b94" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_ScheduleOfShareBasedPaymentAwardOtherThanStockOptionsValuationAssumptionsTableTextBlock_0e13d0e6-5a68-4bbf-8870-d6bd4bf38e64" xlink:href="aciw-20230930.xsd#aciw_ScheduleOfShareBasedPaymentAwardOtherThanStockOptionsValuationAssumptionsTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_54b1ece6-d855-4794-8105-622ba407b1bc" xlink:to="loc_aciw_ScheduleOfShareBasedPaymentAwardOtherThanStockOptionsValuationAssumptionsTableTextBlock_0e13d0e6-5a68-4bbf-8870-d6bd4bf38e64" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfNonvestedRestrictedStockUnitsActivityTableTextBlock_0bca5355-fe40-4f64-aaaf-84348aabffdd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfNonvestedRestrictedStockUnitsActivityTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_54b1ece6-d855-4794-8105-622ba407b1bc" xlink:to="loc_us-gaap_ScheduleOfNonvestedRestrictedStockUnitsActivityTableTextBlock_0bca5355-fe40-4f64-aaaf-84348aabffdd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d26060fc-787b-4356-bfa4-853409af19af" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_54b1ece6-d855-4794-8105-622ba407b1bc" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d26060fc-787b-4356-bfa4-853409af19af" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_ffcf5d63-99d3-4033-b02d-7bfaf2f4e967" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d26060fc-787b-4356-bfa4-853409af19af" xlink:to="loc_us-gaap_AwardTypeAxis_ffcf5d63-99d3-4033-b02d-7bfaf2f4e967" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ffcf5d63-99d3-4033-b02d-7bfaf2f4e967_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_ffcf5d63-99d3-4033-b02d-7bfaf2f4e967" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ffcf5d63-99d3-4033-b02d-7bfaf2f4e967_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_cd1f74e0-4f15-4476-860a-d9db9b887a9a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_ffcf5d63-99d3-4033-b02d-7bfaf2f4e967" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_cd1f74e0-4f15-4476-860a-d9db9b887a9a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_TotalShareholderReturnMember_8e91a2a4-70a3-4f5c-9f92-ca09a1773d6b" xlink:href="aciw-20230930.xsd#aciw_TotalShareholderReturnMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_cd1f74e0-4f15-4476-860a-d9db9b887a9a" xlink:to="loc_aciw_TotalShareholderReturnMember_8e91a2a4-70a3-4f5c-9f92-ca09a1773d6b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_80ef669b-1b4c-452e-8a11-bbc3e644354c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_cd1f74e0-4f15-4476-860a-d9db9b887a9a" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_80ef669b-1b4c-452e-8a11-bbc3e644354c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueAxis_5999c2ea-e142-4cc0-8b0b-e40f3dc5732e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ValuationTechniqueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d26060fc-787b-4356-bfa4-853409af19af" xlink:to="loc_us-gaap_ValuationTechniqueAxis_5999c2ea-e142-4cc0-8b0b-e40f3dc5732e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_5999c2ea-e142-4cc0-8b0b-e40f3dc5732e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationTechniqueAxis_5999c2ea-e142-4cc0-8b0b-e40f3dc5732e" xlink:to="loc_us-gaap_ValuationTechniqueDomain_5999c2ea-e142-4cc0-8b0b-e40f3dc5732e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_5b2c714b-3a06-4cb1-b6b3-996502bc64b5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationTechniqueAxis_5999c2ea-e142-4cc0-8b0b-e40f3dc5732e" xlink:to="loc_us-gaap_ValuationTechniqueDomain_5b2c714b-3a06-4cb1-b6b3-996502bc64b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_MonteCarloSimulationValuationModelMember_7826167d-fed0-47f1-8f93-d677f0170487" xlink:href="aciw-20230930.xsd#aciw_MonteCarloSimulationValuationModelMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_5b2c714b-3a06-4cb1-b6b3-996502bc64b5" xlink:to="loc_aciw_MonteCarloSimulationValuationModelMember_7826167d-fed0-47f1-8f93-d677f0170487" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.aciworldwide.com/role/CondensedConsolidatedFinancialStatementsNarrativeDetails" xlink:type="simple" xlink:href="aciw-20230930.xsd#CondensedConsolidatedFinancialStatementsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.aciworldwide.com/role/CondensedConsolidatedFinancialStatementsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_srt_CondensedFinancialStatementsCaptionsLineItems_e70d516a-3269-4433-bfc4-0a7948e37783" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CondensedFinancialStatementsCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_SettlementFundsBalance_ee35d945-cde6-4ea7-9fd8-56f5742c5d55" xlink:href="aciw-20230930.xsd#aciw_SettlementFundsBalance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_e70d516a-3269-4433-bfc4-0a7948e37783" xlink:to="loc_aciw_SettlementFundsBalance_ee35d945-cde6-4ea7-9fd8-56f5742c5d55" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_2acc152e-974c-46ba-bd15-e5791ddfe30f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_e70d516a-3269-4433-bfc4-0a7948e37783" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_2acc152e-974c-46ba-bd15-e5791ddfe30f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_2f0ef95c-1af3-4798-95a9-71b472211033" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_e70d516a-3269-4433-bfc4-0a7948e37783" xlink:to="loc_us-gaap_LongTermDebtFairValue_2f0ef95c-1af3-4798-95a9-71b472211033" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_46bd7eb5-725e-408a-814c-c2697cb31df7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_e70d516a-3269-4433-bfc4-0a7948e37783" xlink:to="loc_us-gaap_Goodwill_46bd7eb5-725e-408a-814c-c2697cb31df7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireInterestInSubsidiariesAndAffiliates_7368b2ce-91ea-467c-864e-4e6329f7634a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquireInterestInSubsidiariesAndAffiliates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_e70d516a-3269-4433-bfc4-0a7948e37783" xlink:to="loc_us-gaap_PaymentsToAcquireInterestInSubsidiariesAndAffiliates_7368b2ce-91ea-467c-864e-4e6329f7634a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_e1df8f26-98f3-4867-bead-c790e8831a16" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_e70d516a-3269-4433-bfc4-0a7948e37783" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_e1df8f26-98f3-4867-bead-c790e8831a16" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestments_9cf7db77-08e7-4e9f-9fb9-7471ffa12ed7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_e70d516a-3269-4433-bfc4-0a7948e37783" xlink:to="loc_us-gaap_EquityMethodInvestments_9cf7db77-08e7-4e9f-9fb9-7471ffa12ed7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfCondensedFinancialStatementsTable_848ccca0-198c-4c6a-8a86-66d4d3d70426" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ScheduleOfCondensedFinancialStatementsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_e70d516a-3269-4433-bfc4-0a7948e37783" xlink:to="loc_srt_ScheduleOfCondensedFinancialStatementsTable_848ccca0-198c-4c6a-8a86-66d4d3d70426" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_ec68ab26-8b5b-43af-aca5-537e55fcacd2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ScheduleOfCondensedFinancialStatementsTable_848ccca0-198c-4c6a-8a86-66d4d3d70426" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_ec68ab26-8b5b-43af-aca5-537e55fcacd2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ec68ab26-8b5b-43af-aca5-537e55fcacd2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_ec68ab26-8b5b-43af-aca5-537e55fcacd2" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ec68ab26-8b5b-43af-aca5-537e55fcacd2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_bdd70bf3-615e-40d1-a93e-b700f5fa3ec7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_ec68ab26-8b5b-43af-aca5-537e55fcacd2" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_bdd70bf3-615e-40d1-a93e-b700f5fa3ec7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_f1d56e04-a6fd-468c-8276-7daef2dd191b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_bdd70bf3-615e-40d1-a93e-b700f5fa3ec7" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_f1d56e04-a6fd-468c-8276-7daef2dd191b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_7cdca95f-ba07-481d-bf9a-983e9ef77657" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ScheduleOfCondensedFinancialStatementsTable_848ccca0-198c-4c6a-8a86-66d4d3d70426" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_7cdca95f-ba07-481d-bf9a-983e9ef77657" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_7cdca95f-ba07-481d-bf9a-983e9ef77657_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_7cdca95f-ba07-481d-bf9a-983e9ef77657" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_7cdca95f-ba07-481d-bf9a-983e9ef77657_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_ffccbb60-f919-4ca5-8190-f0ac5c5834ed" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_7cdca95f-ba07-481d-bf9a-983e9ef77657" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_ffccbb60-f919-4ca5-8190-f0ac5c5834ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_def8b924-e20a-481e-850c-0fbc5d7df568" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_ffccbb60-f919-4ca5-8190-f0ac5c5834ed" xlink:to="loc_us-gaap_SeniorNotesMember_def8b924-e20a-481e-850c-0fbc5d7df568" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_7a42c3a1-9882-42f2-9dd2-f45432275aaa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ScheduleOfCondensedFinancialStatementsTable_848ccca0-198c-4c6a-8a86-66d4d3d70426" xlink:to="loc_us-gaap_DebtInstrumentAxis_7a42c3a1-9882-42f2-9dd2-f45432275aaa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_7a42c3a1-9882-42f2-9dd2-f45432275aaa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_7a42c3a1-9882-42f2-9dd2-f45432275aaa" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_7a42c3a1-9882-42f2-9dd2-f45432275aaa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_45415333-44fd-43bb-9480-81541a5a80bb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_7a42c3a1-9882-42f2-9dd2-f45432275aaa" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_45415333-44fd-43bb-9480-81541a5a80bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_SeniorNotes5750Due2026Member_bcbadcb3-f2cc-40a8-92ee-258b4d1d8a1e" xlink:href="aciw-20230930.xsd#aciw_SeniorNotes5750Due2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_45415333-44fd-43bb-9480-81541a5a80bb" xlink:to="loc_aciw_SeniorNotes5750Due2026Member_bcbadcb3-f2cc-40a8-92ee-258b4d1d8a1e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_2502757f-934a-4145-b696-fe152e79303f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ScheduleOfCondensedFinancialStatementsTable_848ccca0-198c-4c6a-8a86-66d4d3d70426" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_2502757f-934a-4145-b696-fe152e79303f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_2502757f-934a-4145-b696-fe152e79303f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_2502757f-934a-4145-b696-fe152e79303f" xlink:to="loc_us-gaap_SegmentDomain_2502757f-934a-4145-b696-fe152e79303f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_f2999285-15a1-4375-9ea5-d798f044168c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_2502757f-934a-4145-b696-fe152e79303f" xlink:to="loc_us-gaap_SegmentDomain_f2999285-15a1-4375-9ea5-d798f044168c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_BanksMember_91cfd1e7-fb6b-47ca-95f0-55d3e61bda10" xlink:href="aciw-20230930.xsd#aciw_BanksMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_f2999285-15a1-4375-9ea5-d798f044168c" xlink:to="loc_aciw_BanksMember_91cfd1e7-fb6b-47ca-95f0-55d3e61bda10" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_MerchantsMember_86b5cd3e-f01f-43e6-9b5b-8bfeac6bd08a" xlink:href="aciw-20230930.xsd#aciw_MerchantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_f2999285-15a1-4375-9ea5-d798f044168c" xlink:to="loc_aciw_MerchantsMember_86b5cd3e-f01f-43e6-9b5b-8bfeac6bd08a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_BillersMember_093d29ba-d302-4bbb-bf20-c2b312504797" xlink:href="aciw-20230930.xsd#aciw_BillersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_f2999285-15a1-4375-9ea5-d798f044168c" xlink:to="loc_aciw_BillersMember_093d29ba-d302-4bbb-bf20-c2b312504797" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_886a2196-745b-4c18-a284-8819412b7dc7" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ScheduleOfCondensedFinancialStatementsTable_848ccca0-198c-4c6a-8a86-66d4d3d70426" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_886a2196-745b-4c18-a284-8819412b7dc7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_886a2196-745b-4c18-a284-8819412b7dc7_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_886a2196-745b-4c18-a284-8819412b7dc7" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_886a2196-745b-4c18-a284-8819412b7dc7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_22db0850-2a82-4745-a634-a0a9ec58143c" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_886a2196-745b-4c18-a284-8819412b7dc7" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_22db0850-2a82-4745-a634-a0a9ec58143c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_IndiaPaymentTechnologyAndServicesCompanyMember_3cfec8e8-32e5-40cd-b941-a78b77fe5637" xlink:href="aciw-20230930.xsd#aciw_IndiaPaymentTechnologyAndServicesCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_22db0850-2a82-4745-a634-a0a9ec58143c" xlink:to="loc_aciw_IndiaPaymentTechnologyAndServicesCompanyMember_3cfec8e8-32e5-40cd-b941-a78b77fe5637" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.aciworldwide.com/role/RevenueNarrativeDetails" xlink:type="simple" xlink:href="aciw-20230930.xsd#RevenueNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.aciworldwide.com/role/RevenueNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredRevenueArrangementLineItems_757b8f76-885e-41df-bb68-f599fef75655" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredRevenueArrangementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_5daa773d-4a2c-4b8a-8348-7bfb0e894985" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredRevenueArrangementLineItems_757b8f76-885e-41df-bb68-f599fef75655" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_5daa773d-4a2c-4b8a-8348-7bfb0e894985" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_b82902bc-723b-4017-b41c-f90a1b9db04c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredRevenueArrangementLineItems_757b8f76-885e-41df-bb68-f599fef75655" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_b82902bc-723b-4017-b41c-f90a1b9db04c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_bcdb5103-3b5f-4406-a787-d3752f1cf1ba" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredRevenueArrangementLineItems_757b8f76-885e-41df-bb68-f599fef75655" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_bcdb5103-3b5f-4406-a787-d3752f1cf1ba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_8cefadbe-8949-47cd-809d-bf8154fce615" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredRevenueArrangementLineItems_757b8f76-885e-41df-bb68-f599fef75655" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_8cefadbe-8949-47cd-809d-bf8154fce615" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerPerformanceObligationSatisfiedInPreviousPeriod_cd5417b5-0ac8-429a-9544-151953250e75" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ContractWithCustomerPerformanceObligationSatisfiedInPreviousPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredRevenueArrangementLineItems_757b8f76-885e-41df-bb68-f599fef75655" xlink:to="loc_us-gaap_ContractWithCustomerPerformanceObligationSatisfiedInPreviousPeriod_cd5417b5-0ac8-429a-9544-151953250e75" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredRevenueArrangementByTypeTable_e62ef64e-14f2-47ba-bd1f-67e1d248dcf7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredRevenueArrangementByTypeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DeferredRevenueArrangementLineItems_757b8f76-885e-41df-bb68-f599fef75655" xlink:to="loc_us-gaap_DeferredRevenueArrangementByTypeTable_e62ef64e-14f2-47ba-bd1f-67e1d248dcf7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_56afabba-95b4-4ada-8680-e7a9ebe8394e" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DeferredRevenueArrangementByTypeTable_e62ef64e-14f2-47ba-bd1f-67e1d248dcf7" xlink:to="loc_srt_MajorCustomersAxis_56afabba-95b4-4ada-8680-e7a9ebe8394e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_56afabba-95b4-4ada-8680-e7a9ebe8394e_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_56afabba-95b4-4ada-8680-e7a9ebe8394e" xlink:to="loc_srt_NameOfMajorCustomerDomain_56afabba-95b4-4ada-8680-e7a9ebe8394e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_15413216-91af-4e34-81cd-919c1aa08473" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_56afabba-95b4-4ada-8680-e7a9ebe8394e" xlink:to="loc_srt_NameOfMajorCustomerDomain_15413216-91af-4e34-81cd-919c1aa08473" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_SignificantCustomerMember_8e9fbc8c-75b3-491e-9c56-344e393570fe" xlink:href="aciw-20230930.xsd#aciw_SignificantCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_15413216-91af-4e34-81cd-919c1aa08473" xlink:to="loc_aciw_SignificantCustomerMember_8e9fbc8c-75b3-491e-9c56-344e393570fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_95162441-5daa-4ed1-99c0-c1ce128356bf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DeferredRevenueArrangementByTypeTable_e62ef64e-14f2-47ba-bd1f-67e1d248dcf7" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_95162441-5daa-4ed1-99c0-c1ce128356bf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_95162441-5daa-4ed1-99c0-c1ce128356bf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_95162441-5daa-4ed1-99c0-c1ce128356bf" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_95162441-5daa-4ed1-99c0-c1ce128356bf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_8e06ebf4-997e-4f9b-96bd-3f0e219af31d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_95162441-5daa-4ed1-99c0-c1ce128356bf" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_8e06ebf4-997e-4f9b-96bd-3f0e219af31d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_b7d7aa0a-fdb5-4b0c-baf0-9fb8b0bd9e1a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_8e06ebf4-997e-4f9b-96bd-3f0e219af31d" xlink:to="loc_us-gaap_SalesRevenueNetMember_b7d7aa0a-fdb5-4b0c-baf0-9fb8b0bd9e1a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_a0ef2fa9-4f61-45ef-8238-e4a92c694e53" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DeferredRevenueArrangementByTypeTable_e62ef64e-14f2-47ba-bd1f-67e1d248dcf7" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_a0ef2fa9-4f61-45ef-8238-e4a92c694e53" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_a0ef2fa9-4f61-45ef-8238-e4a92c694e53_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_a0ef2fa9-4f61-45ef-8238-e4a92c694e53" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_a0ef2fa9-4f61-45ef-8238-e4a92c694e53_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_649d90b3-e41e-484c-9736-508b0ea11da7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_a0ef2fa9-4f61-45ef-8238-e4a92c694e53" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_649d90b3-e41e-484c-9736-508b0ea11da7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_fb2dc105-d357-4de7-aa90-132b72915ed5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_649d90b3-e41e-484c-9736-508b0ea11da7" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_fb2dc105-d357-4de7-aa90-132b72915ed5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_609a191a-7bda-4eeb-9587-80022bfbdfe6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DeferredRevenueArrangementByTypeTable_e62ef64e-14f2-47ba-bd1f-67e1d248dcf7" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_609a191a-7bda-4eeb-9587-80022bfbdfe6" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.aciworldwide.com/role/RevenueNarrativeDetails_1" xlink:type="simple" xlink:href="aciw-20230930.xsd#RevenueNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://www.aciworldwide.com/role/RevenueNarrativeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredRevenueArrangementLineItems_757b8f76-885e-41df-bb68-f599fef75655" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredRevenueArrangementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_5daa773d-4a2c-4b8a-8348-7bfb0e894985" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredRevenueArrangementLineItems_757b8f76-885e-41df-bb68-f599fef75655" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_5daa773d-4a2c-4b8a-8348-7bfb0e894985" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_b82902bc-723b-4017-b41c-f90a1b9db04c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredRevenueArrangementLineItems_757b8f76-885e-41df-bb68-f599fef75655" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_b82902bc-723b-4017-b41c-f90a1b9db04c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_bcdb5103-3b5f-4406-a787-d3752f1cf1ba" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredRevenueArrangementLineItems_757b8f76-885e-41df-bb68-f599fef75655" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_bcdb5103-3b5f-4406-a787-d3752f1cf1ba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_8cefadbe-8949-47cd-809d-bf8154fce615" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredRevenueArrangementLineItems_757b8f76-885e-41df-bb68-f599fef75655" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_8cefadbe-8949-47cd-809d-bf8154fce615" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerPerformanceObligationSatisfiedInPreviousPeriod_cd5417b5-0ac8-429a-9544-151953250e75" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ContractWithCustomerPerformanceObligationSatisfiedInPreviousPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredRevenueArrangementLineItems_757b8f76-885e-41df-bb68-f599fef75655" xlink:to="loc_us-gaap_ContractWithCustomerPerformanceObligationSatisfiedInPreviousPeriod_cd5417b5-0ac8-429a-9544-151953250e75" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredRevenueArrangementByTypeTable_e62ef64e-14f2-47ba-bd1f-67e1d248dcf7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredRevenueArrangementByTypeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DeferredRevenueArrangementLineItems_757b8f76-885e-41df-bb68-f599fef75655" xlink:to="loc_us-gaap_DeferredRevenueArrangementByTypeTable_e62ef64e-14f2-47ba-bd1f-67e1d248dcf7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_56afabba-95b4-4ada-8680-e7a9ebe8394e" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DeferredRevenueArrangementByTypeTable_e62ef64e-14f2-47ba-bd1f-67e1d248dcf7" xlink:to="loc_srt_MajorCustomersAxis_56afabba-95b4-4ada-8680-e7a9ebe8394e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_56afabba-95b4-4ada-8680-e7a9ebe8394e_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_56afabba-95b4-4ada-8680-e7a9ebe8394e" xlink:to="loc_srt_NameOfMajorCustomerDomain_56afabba-95b4-4ada-8680-e7a9ebe8394e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_15413216-91af-4e34-81cd-919c1aa08473" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_56afabba-95b4-4ada-8680-e7a9ebe8394e" xlink:to="loc_srt_NameOfMajorCustomerDomain_15413216-91af-4e34-81cd-919c1aa08473" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_SignificantCustomerMember_8e9fbc8c-75b3-491e-9c56-344e393570fe" xlink:href="aciw-20230930.xsd#aciw_SignificantCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_15413216-91af-4e34-81cd-919c1aa08473" xlink:to="loc_aciw_SignificantCustomerMember_8e9fbc8c-75b3-491e-9c56-344e393570fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_95162441-5daa-4ed1-99c0-c1ce128356bf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DeferredRevenueArrangementByTypeTable_e62ef64e-14f2-47ba-bd1f-67e1d248dcf7" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_95162441-5daa-4ed1-99c0-c1ce128356bf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_95162441-5daa-4ed1-99c0-c1ce128356bf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_95162441-5daa-4ed1-99c0-c1ce128356bf" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_95162441-5daa-4ed1-99c0-c1ce128356bf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_8e06ebf4-997e-4f9b-96bd-3f0e219af31d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_95162441-5daa-4ed1-99c0-c1ce128356bf" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_8e06ebf4-997e-4f9b-96bd-3f0e219af31d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_b7d7aa0a-fdb5-4b0c-baf0-9fb8b0bd9e1a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_8e06ebf4-997e-4f9b-96bd-3f0e219af31d" xlink:to="loc_us-gaap_SalesRevenueNetMember_b7d7aa0a-fdb5-4b0c-baf0-9fb8b0bd9e1a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_a0ef2fa9-4f61-45ef-8238-e4a92c694e53" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DeferredRevenueArrangementByTypeTable_e62ef64e-14f2-47ba-bd1f-67e1d248dcf7" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_a0ef2fa9-4f61-45ef-8238-e4a92c694e53" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_a0ef2fa9-4f61-45ef-8238-e4a92c694e53_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_a0ef2fa9-4f61-45ef-8238-e4a92c694e53" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_a0ef2fa9-4f61-45ef-8238-e4a92c694e53_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_649d90b3-e41e-484c-9736-508b0ea11da7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_a0ef2fa9-4f61-45ef-8238-e4a92c694e53" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_649d90b3-e41e-484c-9736-508b0ea11da7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_fb2dc105-d357-4de7-aa90-132b72915ed5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_649d90b3-e41e-484c-9736-508b0ea11da7" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_fb2dc105-d357-4de7-aa90-132b72915ed5" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.aciworldwide.com/role/DivestitureDetails" xlink:type="simple" xlink:href="aciw-20230930.xsd#DivestitureDetails"/>
  <link:definitionLink xlink:role="http://www.aciworldwide.com/role/DivestitureDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_bab27e22-1c63-4460-adb8-b9ca8bf79e8d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_72eefc30-36ff-4a1d-80d6-f9a724eb9df3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_bab27e22-1c63-4460-adb8-b9ca8bf79e8d" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_72eefc30-36ff-4a1d-80d6-f9a724eb9df3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_719e613f-cfe6-49a6-88b1-b6a5f4bc3b36" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_bab27e22-1c63-4460-adb8-b9ca8bf79e8d" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_719e613f-cfe6-49a6-88b1-b6a5f4bc3b36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_TransitionServicesAgreementMigrationPeriod_f7b45143-27c2-4b9b-94f3-520ec7c6b9e2" xlink:href="aciw-20230930.xsd#aciw_TransitionServicesAgreementMigrationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_bab27e22-1c63-4460-adb8-b9ca8bf79e8d" xlink:to="loc_aciw_TransitionServicesAgreementMigrationPeriod_f7b45143-27c2-4b9b-94f3-520ec7c6b9e2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_a1e4d6da-5e73-483a-81ae-ac7e9c8c2142" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_bab27e22-1c63-4460-adb8-b9ca8bf79e8d" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_a1e4d6da-5e73-483a-81ae-ac7e9c8c2142" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_d323dade-cb9c-4af1-b5bb-8f66d9d64ca5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_a1e4d6da-5e73-483a-81ae-ac7e9c8c2142" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_d323dade-cb9c-4af1-b5bb-8f66d9d64ca5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_d323dade-cb9c-4af1-b5bb-8f66d9d64ca5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_d323dade-cb9c-4af1-b5bb-8f66d9d64ca5" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_d323dade-cb9c-4af1-b5bb-8f66d9d64ca5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_627e7bec-84f1-4418-9785-30fde60e6d7c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_d323dade-cb9c-4af1-b5bb-8f66d9d64ca5" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_627e7bec-84f1-4418-9785-30fde60e6d7c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_adacaa31-31c4-4ad9-9e6c-33b61a3610fc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_627e7bec-84f1-4418-9785-30fde60e6d7c" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_adacaa31-31c4-4ad9-9e6c-33b61a3610fc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_93a9b04a-7403-4522-a027-05e6964debe2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_a1e4d6da-5e73-483a-81ae-ac7e9c8c2142" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_93a9b04a-7403-4522-a027-05e6964debe2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_93a9b04a-7403-4522-a027-05e6964debe2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_93a9b04a-7403-4522-a027-05e6964debe2" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_93a9b04a-7403-4522-a027-05e6964debe2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_79b6f2a7-8aca-4127-b944-d4c4a52627e7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_93a9b04a-7403-4522-a027-05e6964debe2" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_79b6f2a7-8aca-4127-b944-d4c4a52627e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_OneEquityPartnersMember_9b77f602-9b4a-4b42-af7f-fad77bc3bbd9" xlink:href="aciw-20230930.xsd#aciw_OneEquityPartnersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_79b6f2a7-8aca-4127-b944-d4c4a52627e7" xlink:to="loc_aciw_OneEquityPartnersMember_9b77f602-9b4a-4b42-af7f-fad77bc3bbd9" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.aciworldwide.com/role/DebtNarrativeDetails" xlink:type="simple" xlink:href="aciw-20230930.xsd#DebtNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.aciworldwide.com/role/DebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_dee0dc1b-e428-4b75-bb99-fc5c2032f493" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_bb0e2430-827d-4242-9019-ef8e25164207" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_dee0dc1b-e428-4b75-bb99-fc5c2032f493" xlink:to="loc_us-gaap_LineOfCredit_bb0e2430-827d-4242-9019-ef8e25164207" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_3ea5f17c-06cd-4e3a-ab45-dc78820f855a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_dee0dc1b-e428-4b75-bb99-fc5c2032f493" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_3ea5f17c-06cd-4e3a-ab45-dc78820f855a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount_59596b4e-f91f-41af-8dc3-b2b9241485ec" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_dee0dc1b-e428-4b75-bb99-fc5c2032f493" xlink:to="loc_us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount_59596b4e-f91f-41af-8dc3-b2b9241485ec" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_DebtInstrumentTermExtension_fc3be5dc-06e3-42d1-9bd8-f8c71091f0b8" xlink:href="aciw-20230930.xsd#aciw_DebtInstrumentTermExtension"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_dee0dc1b-e428-4b75-bb99-fc5c2032f493" xlink:to="loc_aciw_DebtInstrumentTermExtension_fc3be5dc-06e3-42d1-9bd8-f8c71091f0b8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTerm_31d39355-fe1d-47b9-9120-a1e78e104ed5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_dee0dc1b-e428-4b75-bb99-fc5c2032f493" xlink:to="loc_us-gaap_DebtInstrumentTerm_31d39355-fe1d-47b9-9120-a1e78e104ed5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_464ae6f1-755d-4bd4-9ba5-e5cffe9b1407" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_dee0dc1b-e428-4b75-bb99-fc5c2032f493" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_464ae6f1-755d-4bd4-9ba5-e5cffe9b1407" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_f96bc31b-eeb2-4d51-b99f-01bc24ae6cd7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_dee0dc1b-e428-4b75-bb99-fc5c2032f493" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_f96bc31b-eeb2-4d51-b99f-01bc24ae6cd7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_2eb6cbdf-3e81-4e12-9dbd-455e0667816f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_dee0dc1b-e428-4b75-bb99-fc5c2032f493" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_2eb6cbdf-3e81-4e12-9dbd-455e0667816f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd_88b4a96f-a94f-4d39-8d7c-e1a99a31e112" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_dee0dc1b-e428-4b75-bb99-fc5c2032f493" xlink:to="loc_us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd_88b4a96f-a94f-4d39-8d7c-e1a99a31e112" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_DebtInstrumentIssuePricePercentageOfPrincipalAmount_9b132d46-28b0-47ff-b644-16b087a8d198" xlink:href="aciw-20230930.xsd#aciw_DebtInstrumentIssuePricePercentageOfPrincipalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_dee0dc1b-e428-4b75-bb99-fc5c2032f493" xlink:to="loc_aciw_DebtInstrumentIssuePricePercentageOfPrincipalAmount_9b132d46-28b0-47ff-b644-16b087a8d198" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_ee806caa-6c05-47be-a7e8-91aea54a2e1e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_dee0dc1b-e428-4b75-bb99-fc5c2032f493" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_ee806caa-6c05-47be-a7e8-91aea54a2e1e" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity_ed44b29a-03c5-450c-bc67-e3c0c589d5bc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_dee0dc1b-e428-4b75-bb99-fc5c2032f493" xlink:to="loc_us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity_ed44b29a-03c5-450c-bc67-e3c0c589d5bc" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding_e2a57788-6baf-451d-91bc-e49b4282dcf1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_dee0dc1b-e428-4b75-bb99-fc5c2032f493" xlink:to="loc_us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding_e2a57788-6baf-451d-91bc-e49b4282dcf1" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLongTermDebt_712e342a-1916-4ab2-ac91-96366537402c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_dee0dc1b-e428-4b75-bb99-fc5c2032f493" xlink:to="loc_us-gaap_OtherLongTermDebt_712e342a-1916-4ab2-ac91-96366537402c" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_046b24ad-8279-4866-a026-3c11de0dce37" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_dee0dc1b-e428-4b75-bb99-fc5c2032f493" xlink:to="loc_us-gaap_DebtInstrumentTable_046b24ad-8279-4866-a026-3c11de0dce37" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_21062726-aed0-41d7-b4cb-02114579642a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_046b24ad-8279-4866-a026-3c11de0dce37" xlink:to="loc_us-gaap_CreditFacilityAxis_21062726-aed0-41d7-b4cb-02114579642a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_21062726-aed0-41d7-b4cb-02114579642a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_21062726-aed0-41d7-b4cb-02114579642a" xlink:to="loc_us-gaap_CreditFacilityDomain_21062726-aed0-41d7-b4cb-02114579642a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_ae41f61c-a3e2-4cfe-902b-2eaa3f78c24e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_21062726-aed0-41d7-b4cb-02114579642a" xlink:to="loc_us-gaap_CreditFacilityDomain_ae41f61c-a3e2-4cfe-902b-2eaa3f78c24e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_a5464ed0-ace6-4601-ad61-77c462ccaa83" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_ae41f61c-a3e2-4cfe-902b-2eaa3f78c24e" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_a5464ed0-ace6-4601-ad61-77c462ccaa83" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_TermLoansMember_b8ed1ad8-0dac-40f0-ad65-0eda00f3bece" xlink:href="aciw-20230930.xsd#aciw_TermLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_ae41f61c-a3e2-4cfe-902b-2eaa3f78c24e" xlink:to="loc_aciw_TermLoansMember_b8ed1ad8-0dac-40f0-ad65-0eda00f3bece" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_InitialTermLoanMember_3d4a776f-5391-46fa-882f-8018ed24199a" xlink:href="aciw-20230930.xsd#aciw_InitialTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_ae41f61c-a3e2-4cfe-902b-2eaa3f78c24e" xlink:to="loc_aciw_InitialTermLoanMember_3d4a776f-5391-46fa-882f-8018ed24199a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_DelayedDrawTermLoanMember_7ad05a37-ed76-46e0-9e0e-9504b88213fd" xlink:href="aciw-20230930.xsd#aciw_DelayedDrawTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_ae41f61c-a3e2-4cfe-902b-2eaa3f78c24e" xlink:to="loc_aciw_DelayedDrawTermLoanMember_7ad05a37-ed76-46e0-9e0e-9504b88213fd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_6678e979-00a1-4d42-98c5-45ca026b7bac" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_046b24ad-8279-4866-a026-3c11de0dce37" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_6678e979-00a1-4d42-98c5-45ca026b7bac" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_6678e979-00a1-4d42-98c5-45ca026b7bac_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_6678e979-00a1-4d42-98c5-45ca026b7bac" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_6678e979-00a1-4d42-98c5-45ca026b7bac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_fd0d344a-04cc-4808-a020-85d7a84a1d9d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_6678e979-00a1-4d42-98c5-45ca026b7bac" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_fd0d344a-04cc-4808-a020-85d7a84a1d9d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_a526eef9-c4f6-4963-a109-80deeef48403" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_fd0d344a-04cc-4808-a020-85d7a84a1d9d" xlink:to="loc_us-gaap_SeniorNotesMember_a526eef9-c4f6-4963-a109-80deeef48403" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayableOtherPayablesMember_4b3f6865-2c90-46d1-b5eb-81aeb3a1454a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NotesPayableOtherPayablesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_fd0d344a-04cc-4808-a020-85d7a84a1d9d" xlink:to="loc_us-gaap_NotesPayableOtherPayablesMember_4b3f6865-2c90-46d1-b5eb-81aeb3a1454a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeAxis_dcd41d87-e698-4ea8-ab01-7a2edbb9fe8e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShortTermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_046b24ad-8279-4866-a026-3c11de0dce37" xlink:to="loc_us-gaap_ShortTermDebtTypeAxis_dcd41d87-e698-4ea8-ab01-7a2edbb9fe8e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_dcd41d87-e698-4ea8-ab01-7a2edbb9fe8e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_dcd41d87-e698-4ea8-ab01-7a2edbb9fe8e" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_dcd41d87-e698-4ea8-ab01-7a2edbb9fe8e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_0061b2fc-8a30-40ba-991a-12b4fdbee457" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_dcd41d87-e698-4ea8-ab01-7a2edbb9fe8e" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_0061b2fc-8a30-40ba-991a-12b4fdbee457" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_3481e090-acc5-49e6-ab8f-d74498f91d94" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_0061b2fc-8a30-40ba-991a-12b4fdbee457" xlink:to="loc_us-gaap_LetterOfCreditMember_3481e090-acc5-49e6-ab8f-d74498f91d94" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_OverdraftFacilityMember_9cc333a6-6464-49a5-87cc-2ad3601ea4a2" xlink:href="aciw-20230930.xsd#aciw_OverdraftFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_0061b2fc-8a30-40ba-991a-12b4fdbee457" xlink:to="loc_aciw_OverdraftFacilityMember_9cc333a6-6464-49a5-87cc-2ad3601ea4a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_0919f9b6-e51e-4fd9-a240-7cfd00826252" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_046b24ad-8279-4866-a026-3c11de0dce37" xlink:to="loc_us-gaap_DebtInstrumentAxis_0919f9b6-e51e-4fd9-a240-7cfd00826252" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_0919f9b6-e51e-4fd9-a240-7cfd00826252_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_0919f9b6-e51e-4fd9-a240-7cfd00826252" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_0919f9b6-e51e-4fd9-a240-7cfd00826252_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_ef4adb34-c6df-4cbc-90d4-5e9d04cf3c3d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_0919f9b6-e51e-4fd9-a240-7cfd00826252" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_ef4adb34-c6df-4cbc-90d4-5e9d04cf3c3d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_CreditAgreementMember_1ef95ae1-242c-4c17-8f06-5b95ec0d8ba9" xlink:href="aciw-20230930.xsd#aciw_CreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ef4adb34-c6df-4cbc-90d4-5e9d04cf3c3d" xlink:to="loc_aciw_CreditAgreementMember_1ef95ae1-242c-4c17-8f06-5b95ec0d8ba9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_SeniorNotesFivePointSevenFivePercentDueTwoThousandTwentySixMember_dc914efa-7f55-45f3-9974-6e89d1963713" xlink:href="aciw-20230930.xsd#aciw_SeniorNotesFivePointSevenFivePercentDueTwoThousandTwentySixMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ef4adb34-c6df-4cbc-90d4-5e9d04cf3c3d" xlink:to="loc_aciw_SeniorNotesFivePointSevenFivePercentDueTwoThousandTwentySixMember_dc914efa-7f55-45f3-9974-6e89d1963713" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_MultiYearLicenseAgreementMember_4dc285e6-8f5d-4b0f-a7bc-8468030d9600" xlink:href="aciw-20230930.xsd#aciw_MultiYearLicenseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ef4adb34-c6df-4cbc-90d4-5e9d04cf3c3d" xlink:to="loc_aciw_MultiYearLicenseAgreementMember_4dc285e6-8f5d-4b0f-a7bc-8468030d9600" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_9fc8a88b-9812-4ae2-9aa0-1c974bd01bbb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_046b24ad-8279-4866-a026-3c11de0dce37" xlink:to="loc_us-gaap_VariableRateAxis_9fc8a88b-9812-4ae2-9aa0-1c974bd01bbb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_9fc8a88b-9812-4ae2-9aa0-1c974bd01bbb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_9fc8a88b-9812-4ae2-9aa0-1c974bd01bbb" xlink:to="loc_us-gaap_VariableRateDomain_9fc8a88b-9812-4ae2-9aa0-1c974bd01bbb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_3141537b-861a-49f1-bae1-30c7888c12fd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_9fc8a88b-9812-4ae2-9aa0-1c974bd01bbb" xlink:to="loc_us-gaap_VariableRateDomain_3141537b-861a-49f1-bae1-30c7888c12fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalFundsEffectiveSwapRateMember_6cb44ce7-46c9-43f1-8553-48de9248923e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FederalFundsEffectiveSwapRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_3141537b-861a-49f1-bae1-30c7888c12fd" xlink:to="loc_us-gaap_FederalFundsEffectiveSwapRateMember_6cb44ce7-46c9-43f1-8553-48de9248923e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_SecuredOvernightFinancingRateSOFRMember_70094c79-671d-4f9c-a398-c564e71db105" xlink:href="aciw-20230930.xsd#aciw_SecuredOvernightFinancingRateSOFRMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_3141537b-861a-49f1-bae1-30c7888c12fd" xlink:to="loc_aciw_SecuredOvernightFinancingRateSOFRMember_70094c79-671d-4f9c-a398-c564e71db105" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BaseRateMember_11da3650-b473-4c24-b7c3-651a40b40847" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_3141537b-861a-49f1-bae1-30c7888c12fd" xlink:to="loc_us-gaap_BaseRateMember_11da3650-b473-4c24-b7c3-651a40b40847" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_VariableRateOptionsAxis_f2d6c5e8-b86b-4af8-bd7a-7c27f46b2947" xlink:href="aciw-20230930.xsd#aciw_VariableRateOptionsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_046b24ad-8279-4866-a026-3c11de0dce37" xlink:to="loc_aciw_VariableRateOptionsAxis_f2d6c5e8-b86b-4af8-bd7a-7c27f46b2947" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_VariableRateOptionsDomain_f2d6c5e8-b86b-4af8-bd7a-7c27f46b2947_default" xlink:href="aciw-20230930.xsd#aciw_VariableRateOptionsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_aciw_VariableRateOptionsAxis_f2d6c5e8-b86b-4af8-bd7a-7c27f46b2947" xlink:to="loc_aciw_VariableRateOptionsDomain_f2d6c5e8-b86b-4af8-bd7a-7c27f46b2947_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_VariableRateOptionsDomain_00bbcae0-1823-4460-a252-51776187a103" xlink:href="aciw-20230930.xsd#aciw_VariableRateOptionsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_aciw_VariableRateOptionsAxis_f2d6c5e8-b86b-4af8-bd7a-7c27f46b2947" xlink:to="loc_aciw_VariableRateOptionsDomain_00bbcae0-1823-4460-a252-51776187a103" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_VariableRateOptionOneMember_d8a02a2b-7de6-4054-a8aa-65f6dfee75a7" xlink:href="aciw-20230930.xsd#aciw_VariableRateOptionOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aciw_VariableRateOptionsDomain_00bbcae0-1823-4460-a252-51776187a103" xlink:to="loc_aciw_VariableRateOptionOneMember_d8a02a2b-7de6-4054-a8aa-65f6dfee75a7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_VariableRateOptionTwoMember_e5d9c501-5200-4e2f-8793-f434f4b5ac40" xlink:href="aciw-20230930.xsd#aciw_VariableRateOptionTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aciw_VariableRateOptionsDomain_00bbcae0-1823-4460-a252-51776187a103" xlink:to="loc_aciw_VariableRateOptionTwoMember_e5d9c501-5200-4e2f-8793-f434f4b5ac40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_b6e068c1-11ff-4612-90c5-7d3e8bf52521" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_046b24ad-8279-4866-a026-3c11de0dce37" xlink:to="loc_srt_RangeAxis_b6e068c1-11ff-4612-90c5-7d3e8bf52521" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_b6e068c1-11ff-4612-90c5-7d3e8bf52521_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_b6e068c1-11ff-4612-90c5-7d3e8bf52521" xlink:to="loc_srt_RangeMember_b6e068c1-11ff-4612-90c5-7d3e8bf52521_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_2eb2f8cb-b65e-464c-926c-d432a88b37ca" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_b6e068c1-11ff-4612-90c5-7d3e8bf52521" xlink:to="loc_srt_RangeMember_2eb2f8cb-b65e-464c-926c-d432a88b37ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_cd4a6ed6-7bc2-45c0-b1df-d59954074680" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_2eb2f8cb-b65e-464c-926c-d432a88b37ca" xlink:to="loc_srt_MinimumMember_cd4a6ed6-7bc2-45c0-b1df-d59954074680" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_ba33f9e7-98df-4a97-b76d-5872e4992edc" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_2eb2f8cb-b65e-464c-926c-d432a88b37ca" xlink:to="loc_srt_MaximumMember_ba33f9e7-98df-4a97-b76d-5872e4992edc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_3b2d872f-e276-4f68-a0ed-2b998e12b0d1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_046b24ad-8279-4866-a026-3c11de0dce37" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_3b2d872f-e276-4f68-a0ed-2b998e12b0d1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_3b2d872f-e276-4f68-a0ed-2b998e12b0d1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_3b2d872f-e276-4f68-a0ed-2b998e12b0d1" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_3b2d872f-e276-4f68-a0ed-2b998e12b0d1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_b08c4de0-61d1-42c0-8f81-78ca48663426" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_3b2d872f-e276-4f68-a0ed-2b998e12b0d1" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_b08c4de0-61d1-42c0-8f81-78ca48663426" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCurrentLiabilitiesMember_0996d7cc-cc6c-4786-a6e1-90d8c511b1a5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherCurrentLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_b08c4de0-61d1-42c0-8f81-78ca48663426" xlink:to="loc_us-gaap_OtherCurrentLiabilitiesMember_0996d7cc-cc6c-4786-a6e1-90d8c511b1a5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoncurrentLiabilitiesMember_32ca00d7-6239-458a-a395-ff56725e1d26" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherNoncurrentLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_b08c4de0-61d1-42c0-8f81-78ca48663426" xlink:to="loc_us-gaap_OtherNoncurrentLiabilitiesMember_32ca00d7-6239-458a-a395-ff56725e1d26" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.aciworldwide.com/role/DebtScheduleofTotalDebtDetails" xlink:type="simple" xlink:href="aciw-20230930.xsd#DebtScheduleofTotalDebtDetails"/>
  <link:definitionLink xlink:role="http://www.aciworldwide.com/role/DebtScheduleofTotalDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_83655eef-a3f7-4ac0-aa3d-4bda8d303505" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_69ce4e36-8818-4201-b20b-715c97176995" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_83655eef-a3f7-4ac0-aa3d-4bda8d303505" xlink:to="loc_us-gaap_LongTermDebt_69ce4e36-8818-4201-b20b-715c97176995" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_87c32a97-db0c-4796-a33d-4eb87662278d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_83655eef-a3f7-4ac0-aa3d-4bda8d303505" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_87c32a97-db0c-4796-a33d-4eb87662278d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_22af5bd0-5517-49b2-a425-c2b9b42e6b54" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_83655eef-a3f7-4ac0-aa3d-4bda8d303505" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_22af5bd0-5517-49b2-a425-c2b9b42e6b54" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_6e74cabb-d841-438e-9c83-f0da9a7b4115" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_83655eef-a3f7-4ac0-aa3d-4bda8d303505" xlink:to="loc_us-gaap_LongTermDebtCurrent_6e74cabb-d841-438e-9c83-f0da9a7b4115" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsCurrentNet_5632cd2d-fbfb-45f2-b07a-d66bf80b33d8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredFinanceCostsCurrentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_83655eef-a3f7-4ac0-aa3d-4bda8d303505" xlink:to="loc_us-gaap_DeferredFinanceCostsCurrentNet_5632cd2d-fbfb-45f2-b07a-d66bf80b33d8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_3a0d636b-27f7-4407-8b66-9868cd0de25c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_83655eef-a3f7-4ac0-aa3d-4bda8d303505" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_3a0d636b-27f7-4407-8b66-9868cd0de25c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_b53c52eb-650b-4284-af88-67c9d80c9998" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_83655eef-a3f7-4ac0-aa3d-4bda8d303505" xlink:to="loc_us-gaap_DebtInstrumentTable_b53c52eb-650b-4284-af88-67c9d80c9998" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_51503571-368a-4f28-bbb1-ed8004d88ab2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b53c52eb-650b-4284-af88-67c9d80c9998" xlink:to="loc_us-gaap_CreditFacilityAxis_51503571-368a-4f28-bbb1-ed8004d88ab2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_51503571-368a-4f28-bbb1-ed8004d88ab2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_51503571-368a-4f28-bbb1-ed8004d88ab2" xlink:to="loc_us-gaap_CreditFacilityDomain_51503571-368a-4f28-bbb1-ed8004d88ab2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_8f0955c1-f2f2-4dc9-aea4-df30514f5f49" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_51503571-368a-4f28-bbb1-ed8004d88ab2" xlink:to="loc_us-gaap_CreditFacilityDomain_8f0955c1-f2f2-4dc9-aea4-df30514f5f49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_TermLoansMember_f857faba-cd8e-47fd-bcdd-bb9540c799f7" xlink:href="aciw-20230930.xsd#aciw_TermLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_8f0955c1-f2f2-4dc9-aea4-df30514f5f49" xlink:to="loc_aciw_TermLoansMember_f857faba-cd8e-47fd-bcdd-bb9540c799f7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_ce300227-8a5b-4b8a-ba88-cae33bf8d0bc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_8f0955c1-f2f2-4dc9-aea4-df30514f5f49" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_ce300227-8a5b-4b8a-ba88-cae33bf8d0bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_51914ae0-a9c2-4d7d-a2bc-6dc3ee9624c0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b53c52eb-650b-4284-af88-67c9d80c9998" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_51914ae0-a9c2-4d7d-a2bc-6dc3ee9624c0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_51914ae0-a9c2-4d7d-a2bc-6dc3ee9624c0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_51914ae0-a9c2-4d7d-a2bc-6dc3ee9624c0" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_51914ae0-a9c2-4d7d-a2bc-6dc3ee9624c0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_b0987efe-d09f-4a94-810b-4782fdfa588e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_51914ae0-a9c2-4d7d-a2bc-6dc3ee9624c0" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_b0987efe-d09f-4a94-810b-4782fdfa588e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_09d0b63a-e35c-4e13-a125-f9e849de110d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_b0987efe-d09f-4a94-810b-4782fdfa588e" xlink:to="loc_us-gaap_LineOfCreditMember_09d0b63a-e35c-4e13-a125-f9e849de110d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_bfb825fe-ad6c-4d7c-a562-87134c6e48d5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_b0987efe-d09f-4a94-810b-4782fdfa588e" xlink:to="loc_us-gaap_SeniorNotesMember_bfb825fe-ad6c-4d7c-a562-87134c6e48d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_dbb28607-55c3-478f-b17e-fa7f92557a68" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b53c52eb-650b-4284-af88-67c9d80c9998" xlink:to="loc_us-gaap_DebtInstrumentAxis_dbb28607-55c3-478f-b17e-fa7f92557a68" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_dbb28607-55c3-478f-b17e-fa7f92557a68_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_dbb28607-55c3-478f-b17e-fa7f92557a68" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_dbb28607-55c3-478f-b17e-fa7f92557a68_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_fa5d39fa-e9c8-4fa8-a84d-75e0b2267b98" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_dbb28607-55c3-478f-b17e-fa7f92557a68" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_fa5d39fa-e9c8-4fa8-a84d-75e0b2267b98" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_SeniorNotesFivePointSevenFivePercentDueTwoThousandTwentySixMember_8273ceda-521a-4238-82c0-7953f7572950" xlink:href="aciw-20230930.xsd#aciw_SeniorNotesFivePointSevenFivePercentDueTwoThousandTwentySixMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_fa5d39fa-e9c8-4fa8-a84d-75e0b2267b98" xlink:to="loc_aciw_SeniorNotesFivePointSevenFivePercentDueTwoThousandTwentySixMember_8273ceda-521a-4238-82c0-7953f7572950" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.aciworldwide.com/role/SoftwareandOtherIntangibleAssetsScheduleofCarryingAmountandAccumulatedAmortizationDetails" xlink:type="simple" xlink:href="aciw-20230930.xsd#SoftwareandOtherIntangibleAssetsScheduleofCarryingAmountandAccumulatedAmortizationDetails"/>
  <link:definitionLink xlink:role="http://www.aciworldwide.com/role/SoftwareandOtherIntangibleAssetsScheduleofCarryingAmountandAccumulatedAmortizationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_38ef03ab-b7b1-4c08-90d7-8cf5d8be9b24" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_3722735e-d9f8-461e-963b-20ad0c084a04" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_38ef03ab-b7b1-4c08-90d7-8cf5d8be9b24" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_3722735e-d9f8-461e-963b-20ad0c084a04" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_d9aa0ed6-fcb1-4f07-ae0e-701202230b47" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_38ef03ab-b7b1-4c08-90d7-8cf5d8be9b24" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_d9aa0ed6-fcb1-4f07-ae0e-701202230b47" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_1394cb42-5b94-4a8b-ae49-6f892c613eaa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_38ef03ab-b7b1-4c08-90d7-8cf5d8be9b24" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_1394cb42-5b94-4a8b-ae49-6f892c613eaa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_c3d7fa9e-a2dc-4fb6-bcd1-91ac413ce967" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_38ef03ab-b7b1-4c08-90d7-8cf5d8be9b24" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_c3d7fa9e-a2dc-4fb6-bcd1-91ac413ce967" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_776f3332-2390-4b52-aead-2c8d6979efec" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_c3d7fa9e-a2dc-4fb6-bcd1-91ac413ce967" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_776f3332-2390-4b52-aead-2c8d6979efec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_776f3332-2390-4b52-aead-2c8d6979efec_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_776f3332-2390-4b52-aead-2c8d6979efec" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_776f3332-2390-4b52-aead-2c8d6979efec_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_fc4ad723-7a02-4bd9-940d-c692a1b3d1e2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_776f3332-2390-4b52-aead-2c8d6979efec" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_fc4ad723-7a02-4bd9-940d-c692a1b3d1e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_SoftwareAcquiredOrDevelopedForInternalUseMember_91844e96-5b35-43f4-a950-f631e1342d43" xlink:href="aciw-20230930.xsd#aciw_SoftwareAcquiredOrDevelopedForInternalUseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_fc4ad723-7a02-4bd9-940d-c692a1b3d1e2" xlink:to="loc_aciw_SoftwareAcquiredOrDevelopedForInternalUseMember_91844e96-5b35-43f4-a950-f631e1342d43" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_OtherFiniteLivedIntangibleAssetsMember_929b5fc6-8417-465f-afd5-7bae36241759" xlink:href="aciw-20230930.xsd#aciw_OtherFiniteLivedIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_fc4ad723-7a02-4bd9-940d-c692a1b3d1e2" xlink:to="loc_aciw_OtherFiniteLivedIntangibleAssetsMember_929b5fc6-8417-465f-afd5-7bae36241759" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_2ed92211-ec7f-45f4-8a3f-de91dbf77d8e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aciw_OtherFiniteLivedIntangibleAssetsMember_929b5fc6-8417-465f-afd5-7bae36241759" xlink:to="loc_us-gaap_CustomerRelationshipsMember_2ed92211-ec7f-45f4-8a3f-de91dbf77d8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TrademarksAndTradeNamesMember_4408c028-7c66-431a-b65e-2cb1c5fe4880" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TrademarksAndTradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aciw_OtherFiniteLivedIntangibleAssetsMember_929b5fc6-8417-465f-afd5-7bae36241759" xlink:to="loc_us-gaap_TrademarksAndTradeNamesMember_4408c028-7c66-431a-b65e-2cb1c5fe4880" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.aciworldwide.com/role/SoftwareandOtherIntangibleAssetsNarrativeDetails" xlink:type="simple" xlink:href="aciw-20230930.xsd#SoftwareandOtherIntangibleAssetsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.aciworldwide.com/role/SoftwareandOtherIntangibleAssetsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_403b418c-9a89-430b-8094-114f3cf83ac8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_14b009f3-e2c6-48db-a19f-9d4194895464" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_403b418c-9a89-430b-8094-114f3cf83ac8" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_14b009f3-e2c6-48db-a19f-9d4194895464" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedComputerSoftwareAmortization1_2dbfc8cd-6e74-4da9-90fd-cf77f99e6078" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CapitalizedComputerSoftwareAmortization1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_403b418c-9a89-430b-8094-114f3cf83ac8" xlink:to="loc_us-gaap_CapitalizedComputerSoftwareAmortization1_2dbfc8cd-6e74-4da9-90fd-cf77f99e6078" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_27c9535a-017c-4570-abe2-422cd9434464" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_403b418c-9a89-430b-8094-114f3cf83ac8" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_27c9535a-017c-4570-abe2-422cd9434464" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_39f2843c-26eb-43b9-b940-a0c032bf8a1f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_403b418c-9a89-430b-8094-114f3cf83ac8" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_39f2843c-26eb-43b9-b940-a0c032bf8a1f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_a914dce6-5c92-4504-a32c-4e9cea2a6db8" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_39f2843c-26eb-43b9-b940-a0c032bf8a1f" xlink:to="loc_srt_RangeAxis_a914dce6-5c92-4504-a32c-4e9cea2a6db8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_a914dce6-5c92-4504-a32c-4e9cea2a6db8_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_a914dce6-5c92-4504-a32c-4e9cea2a6db8" xlink:to="loc_srt_RangeMember_a914dce6-5c92-4504-a32c-4e9cea2a6db8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_072c04cb-1575-4e3f-9540-29133697d994" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_a914dce6-5c92-4504-a32c-4e9cea2a6db8" xlink:to="loc_srt_RangeMember_072c04cb-1575-4e3f-9540-29133697d994" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_3f37e817-86da-4645-976f-1d4510d09379" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_072c04cb-1575-4e3f-9540-29133697d994" xlink:to="loc_srt_MinimumMember_3f37e817-86da-4645-976f-1d4510d09379" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_984ef42c-c06a-4018-a806-537f04abf9e3" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_072c04cb-1575-4e3f-9540-29133697d994" xlink:to="loc_srt_MaximumMember_984ef42c-c06a-4018-a806-537f04abf9e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_bfaa78e6-8d63-4b51-8cbf-65d6a043bb98" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_39f2843c-26eb-43b9-b940-a0c032bf8a1f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_bfaa78e6-8d63-4b51-8cbf-65d6a043bb98" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_bfaa78e6-8d63-4b51-8cbf-65d6a043bb98_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_bfaa78e6-8d63-4b51-8cbf-65d6a043bb98" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_bfaa78e6-8d63-4b51-8cbf-65d6a043bb98_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c983fb89-09ae-49e3-bf3f-bd9f14d6d60a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_bfaa78e6-8d63-4b51-8cbf-65d6a043bb98" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c983fb89-09ae-49e3-bf3f-bd9f14d6d60a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_SoftwareAcquiredOrDevelopedForInternalUseMember_5cfa90cf-49a1-4718-a0af-f1a9a8c366ea" xlink:href="aciw-20230930.xsd#aciw_SoftwareAcquiredOrDevelopedForInternalUseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c983fb89-09ae-49e3-bf3f-bd9f14d6d60a" xlink:to="loc_aciw_SoftwareAcquiredOrDevelopedForInternalUseMember_5cfa90cf-49a1-4718-a0af-f1a9a8c366ea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_SoftwareMarketedForExternalSaleMember_89ccfe94-0fb8-4063-8057-6cb42d041c21" xlink:href="aciw-20230930.xsd#aciw_SoftwareMarketedForExternalSaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c983fb89-09ae-49e3-bf3f-bd9f14d6d60a" xlink:to="loc_aciw_SoftwareMarketedForExternalSaleMember_89ccfe94-0fb8-4063-8057-6cb42d041c21" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.aciworldwide.com/role/SoftwareandOtherIntangibleAssetsScheduleofEstimatedAmortizationExpenseDetails" xlink:type="simple" xlink:href="aciw-20230930.xsd#SoftwareandOtherIntangibleAssetsScheduleofEstimatedAmortizationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.aciworldwide.com/role/SoftwareandOtherIntangibleAssetsScheduleofEstimatedAmortizationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_ed75cc72-e13b-45a4-9fba-8ab97e789151" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_b5d7be1f-b198-4049-a0cf-271688b4777b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_ed75cc72-e13b-45a4-9fba-8ab97e789151" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_b5d7be1f-b198-4049-a0cf-271688b4777b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_a1598031-260c-4c76-ba92-e1a6ca807da1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_ed75cc72-e13b-45a4-9fba-8ab97e789151" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_a1598031-260c-4c76-ba92-e1a6ca807da1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_07d2d534-3b63-4e95-99cd-58ddd7689740" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_ed75cc72-e13b-45a4-9fba-8ab97e789151" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_07d2d534-3b63-4e95-99cd-58ddd7689740" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_b543e77a-d388-42ac-9c4f-56f2bdca25be" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_ed75cc72-e13b-45a4-9fba-8ab97e789151" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_b543e77a-d388-42ac-9c4f-56f2bdca25be" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_aa2a2369-eb87-47b9-8c24-919f2521d0a6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_ed75cc72-e13b-45a4-9fba-8ab97e789151" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_aa2a2369-eb87-47b9-8c24-919f2521d0a6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_FiniteLivedIntangibleAssetExpectedAmortizationAfterYearFour_dc9948e4-1824-4c30-9c6c-9727e995c72e" xlink:href="aciw-20230930.xsd#aciw_FiniteLivedIntangibleAssetExpectedAmortizationAfterYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_ed75cc72-e13b-45a4-9fba-8ab97e789151" xlink:to="loc_aciw_FiniteLivedIntangibleAssetExpectedAmortizationAfterYearFour_dc9948e4-1824-4c30-9c6c-9727e995c72e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_e425ee6e-17d9-41f7-8d28-107fb03892b3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_ed75cc72-e13b-45a4-9fba-8ab97e789151" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_e425ee6e-17d9-41f7-8d28-107fb03892b3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_2c12a2b8-5872-489d-b7d3-1aee43d1d44d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_ed75cc72-e13b-45a4-9fba-8ab97e789151" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_2c12a2b8-5872-489d-b7d3-1aee43d1d44d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_8c2169be-e2ca-4ce6-ad33-48897c8b656e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_2c12a2b8-5872-489d-b7d3-1aee43d1d44d" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_8c2169be-e2ca-4ce6-ad33-48897c8b656e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_8c2169be-e2ca-4ce6-ad33-48897c8b656e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_8c2169be-e2ca-4ce6-ad33-48897c8b656e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_8c2169be-e2ca-4ce6-ad33-48897c8b656e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_a5cfa433-6b3f-4e6e-9dcd-d43fd0f78b26" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_8c2169be-e2ca-4ce6-ad33-48897c8b656e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_a5cfa433-6b3f-4e6e-9dcd-d43fd0f78b26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerSoftwareIntangibleAssetMember_e5f7ca87-37c3-41b5-a115-8748d656e211" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ComputerSoftwareIntangibleAssetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_a5cfa433-6b3f-4e6e-9dcd-d43fd0f78b26" xlink:to="loc_us-gaap_ComputerSoftwareIntangibleAssetMember_e5f7ca87-37c3-41b5-a115-8748d656e211" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_e53fa3c0-9f48-4688-ac98-cd9d5f7e0f4a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_a5cfa433-6b3f-4e6e-9dcd-d43fd0f78b26" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_e53fa3c0-9f48-4688-ac98-cd9d5f7e0f4a" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.aciworldwide.com/role/StockBasedCompensationPlansNarrativeDetails" xlink:type="simple" xlink:href="aciw-20230930.xsd#StockBasedCompensationPlansNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.aciworldwide.com/role/StockBasedCompensationPlansNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_abcd445e-165f-4a46-b77a-150a27dfb497" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_32634760-dd9d-4b94-8873-6e339a058ec5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_abcd445e-165f-4a46-b77a-150a27dfb497" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_32634760-dd9d-4b94-8873-6e339a058ec5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_2441e68a-7cbd-4261-a4f1-f4dc27ab298f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_abcd445e-165f-4a46-b77a-150a27dfb497" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_2441e68a-7cbd-4261-a4f1-f4dc27ab298f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_c3efe753-be83-42a4-9016-1f0b938165ab" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_abcd445e-165f-4a46-b77a-150a27dfb497" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_c3efe753-be83-42a4-9016-1f0b938165ab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_e101f5ee-2f68-46cc-bfa7-90302ad1136e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_abcd445e-165f-4a46-b77a-150a27dfb497" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_e101f5ee-2f68-46cc-bfa7-90302ad1136e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_ShareBasedCompensationArrangementsByShareBasedPaymentAwardTotalShareholderReturnMultiplier_1431efa7-fe45-4f54-a5d0-040fcd1372e6" xlink:href="aciw-20230930.xsd#aciw_ShareBasedCompensationArrangementsByShareBasedPaymentAwardTotalShareholderReturnMultiplier"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_abcd445e-165f-4a46-b77a-150a27dfb497" xlink:to="loc_aciw_ShareBasedCompensationArrangementsByShareBasedPaymentAwardTotalShareholderReturnMultiplier_1431efa7-fe45-4f54-a5d0-040fcd1372e6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_ShareBasedCompensationArrangementsByShareBasedPaymentAwardPerformanceSharesMaximumTarget_f840bf87-e4ea-4217-a40a-81044bedd2da" xlink:href="aciw-20230930.xsd#aciw_ShareBasedCompensationArrangementsByShareBasedPaymentAwardPerformanceSharesMaximumTarget"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_abcd445e-165f-4a46-b77a-150a27dfb497" xlink:to="loc_aciw_ShareBasedCompensationArrangementsByShareBasedPaymentAwardPerformanceSharesMaximumTarget_f840bf87-e4ea-4217-a40a-81044bedd2da" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsIssuedInPeriod_21540631-ab33-4fb2-92d8-20e7d2b2320b" xlink:href="aciw-20230930.xsd#aciw_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsIssuedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_abcd445e-165f-4a46-b77a-150a27dfb497" xlink:to="loc_aciw_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsIssuedInPeriod_21540631-ab33-4fb2-92d8-20e7d2b2320b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_c9af9dda-9188-49cf-9ed3-e8f4d0c9867a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_abcd445e-165f-4a46-b77a-150a27dfb497" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_c9af9dda-9188-49cf-9ed3-e8f4d0c9867a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_e92d8167-12b2-4e72-a682-9abe823667f2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_abcd445e-165f-4a46-b77a-150a27dfb497" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_e92d8167-12b2-4e72-a682-9abe823667f2" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_f1adf586-0c7f-4441-b6b0-24331b3bd795" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_abcd445e-165f-4a46-b77a-150a27dfb497" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_f1adf586-0c7f-4441-b6b0-24331b3bd795" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_1eb9f3d9-d5ee-426e-a4d1-d70cc32d87e9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_abcd445e-165f-4a46-b77a-150a27dfb497" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_1eb9f3d9-d5ee-426e-a4d1-d70cc32d87e9" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_7a44df78-5798-4dfb-826c-d048ad612c2d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_abcd445e-165f-4a46-b77a-150a27dfb497" xlink:to="loc_us-gaap_ShareBasedCompensation_7a44df78-5798-4dfb-826c-d048ad612c2d" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_95453a9a-0313-4323-bf73-05c3dfcbcbe2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_abcd445e-165f-4a46-b77a-150a27dfb497" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_95453a9a-0313-4323-bf73-05c3dfcbcbe2" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_130a00cc-07b1-419d-b966-073b6f01c7c3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_abcd445e-165f-4a46-b77a-150a27dfb497" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_130a00cc-07b1-419d-b966-073b6f01c7c3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_f81239bf-c100-4df9-8e78-96ebdff61f29" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_130a00cc-07b1-419d-b966-073b6f01c7c3" xlink:to="loc_us-gaap_PlanNameAxis_f81239bf-c100-4df9-8e78-96ebdff61f29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_f81239bf-c100-4df9-8e78-96ebdff61f29_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_f81239bf-c100-4df9-8e78-96ebdff61f29" xlink:to="loc_us-gaap_PlanNameDomain_f81239bf-c100-4df9-8e78-96ebdff61f29_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_01e172e6-cf7d-49ed-8c6f-f379f754b742" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_f81239bf-c100-4df9-8e78-96ebdff61f29" xlink:to="loc_us-gaap_PlanNameDomain_01e172e6-cf7d-49ed-8c6f-f379f754b742" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_EmployeeStockPurchasePlanTwentySeventeenMember_91fc1b6c-7cb7-446d-a30a-a5aa6a5cb100" xlink:href="aciw-20230930.xsd#aciw_EmployeeStockPurchasePlanTwentySeventeenMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_01e172e6-cf7d-49ed-8c6f-f379f754b742" xlink:to="loc_aciw_EmployeeStockPurchasePlanTwentySeventeenMember_91fc1b6c-7cb7-446d-a30a-a5aa6a5cb100" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_68811c20-104d-4f71-a902-67b217a8a028" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_130a00cc-07b1-419d-b966-073b6f01c7c3" xlink:to="loc_us-gaap_AwardTypeAxis_68811c20-104d-4f71-a902-67b217a8a028" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_68811c20-104d-4f71-a902-67b217a8a028_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_68811c20-104d-4f71-a902-67b217a8a028" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_68811c20-104d-4f71-a902-67b217a8a028_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9ce78b69-f9cd-4b32-955e-7a79b658399b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_68811c20-104d-4f71-a902-67b217a8a028" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9ce78b69-f9cd-4b32-955e-7a79b658399b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_7f80a8c0-6c9c-445d-b336-b0473e8f1835" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9ce78b69-f9cd-4b32-955e-7a79b658399b" xlink:to="loc_us-gaap_EmployeeStockOptionMember_7f80a8c0-6c9c-445d-b336-b0473e8f1835" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_TotalShareholderReturnMember_3a9a6733-b32f-4260-95de-d536e1e1cd6c" xlink:href="aciw-20230930.xsd#aciw_TotalShareholderReturnMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9ce78b69-f9cd-4b32-955e-7a79b658399b" xlink:to="loc_aciw_TotalShareholderReturnMember_3a9a6733-b32f-4260-95de-d536e1e1cd6c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_c25ca335-784c-4e13-bf24-d6d1fc8dfed7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9ce78b69-f9cd-4b32-955e-7a79b658399b" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_c25ca335-784c-4e13-bf24-d6d1fc8dfed7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_9324dd00-3a70-4119-8e1e-a61a38d572d3" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_130a00cc-07b1-419d-b966-073b6f01c7c3" xlink:to="loc_srt_RangeAxis_9324dd00-3a70-4119-8e1e-a61a38d572d3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_9324dd00-3a70-4119-8e1e-a61a38d572d3_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_9324dd00-3a70-4119-8e1e-a61a38d572d3" xlink:to="loc_srt_RangeMember_9324dd00-3a70-4119-8e1e-a61a38d572d3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_896e336d-9e68-47f3-83c8-5706f08271a4" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_9324dd00-3a70-4119-8e1e-a61a38d572d3" xlink:to="loc_srt_RangeMember_896e336d-9e68-47f3-83c8-5706f08271a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_17f7b7ad-b28b-4af5-a6a5-aa9fcc9bc715" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_896e336d-9e68-47f3-83c8-5706f08271a4" xlink:to="loc_srt_MinimumMember_17f7b7ad-b28b-4af5-a6a5-aa9fcc9bc715" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_faef459b-466f-4f5d-82d6-1e760794699b" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_896e336d-9e68-47f3-83c8-5706f08271a4" xlink:to="loc_srt_MaximumMember_faef459b-466f-4f5d-82d6-1e760794699b" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.aciworldwide.com/role/StockBasedCompensationPlansScheduleofNonvestedTotalShareholderReturnAwardsTSRsDetails" xlink:type="simple" xlink:href="aciw-20230930.xsd#StockBasedCompensationPlansScheduleofNonvestedTotalShareholderReturnAwardsTSRsDetails"/>
  <link:definitionLink xlink:role="http://www.aciworldwide.com/role/StockBasedCompensationPlansScheduleofNonvestedTotalShareholderReturnAwardsTSRsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6de112b6-0fe8-473a-aab2-5d359f847bfd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_a4e81125-4b6f-4d0e-940e-07772bc47096" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6de112b6-0fe8-473a-aab2-5d359f847bfd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_a4e81125-4b6f-4d0e-940e-07772bc47096" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_c4580806-af6d-4ee6-8b2a-1d59ac21760f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_a4e81125-4b6f-4d0e-940e-07772bc47096" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_c4580806-af6d-4ee6-8b2a-1d59ac21760f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_fb58c5a5-9159-420a-81d6-cfabb088249c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_a4e81125-4b6f-4d0e-940e-07772bc47096" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_fb58c5a5-9159-420a-81d6-cfabb088249c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_e452aaf2-c269-44c5-a48c-065eba9f5255" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_a4e81125-4b6f-4d0e-940e-07772bc47096" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_e452aaf2-c269-44c5-a48c-065eba9f5255" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsChangeInPayoutRate_ff798387-f904-4b74-8951-e47b86e650fe" xlink:href="aciw-20230930.xsd#aciw_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsChangeInPayoutRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_a4e81125-4b6f-4d0e-940e-07772bc47096" xlink:to="loc_aciw_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsChangeInPayoutRate_ff798387-f904-4b74-8951-e47b86e650fe" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_62b78f78-a861-4e44-9af6-414958cfe250" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_eb1f3baf-bc4c-4d24-890b-97113dde0866" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6de112b6-0fe8-473a-aab2-5d359f847bfd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_eb1f3baf-bc4c-4d24-890b-97113dde0866" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_ba0ba744-e90b-41b7-b285-69e09d1c5282" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_eb1f3baf-bc4c-4d24-890b-97113dde0866" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_ba0ba744-e90b-41b7-b285-69e09d1c5282" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_2ff62578-a2ba-4ea2-a4f8-7f2bcc26070f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_eb1f3baf-bc4c-4d24-890b-97113dde0866" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_2ff62578-a2ba-4ea2-a4f8-7f2bcc26070f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_f693b3da-dafb-4fcc-ae16-0589a3b39c9a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_eb1f3baf-bc4c-4d24-890b-97113dde0866" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_f693b3da-dafb-4fcc-ae16-0589a3b39c9a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsChangeInPayoutRateWeightedAverageGrantDateFairValue_5de4c24f-a8a9-4520-9c75-9161963c67b3" xlink:href="aciw-20230930.xsd#aciw_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsChangeInPayoutRateWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_eb1f3baf-bc4c-4d24-890b-97113dde0866" xlink:to="loc_aciw_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsChangeInPayoutRateWeightedAverageGrantDateFairValue_5de4c24f-a8a9-4520-9c75-9161963c67b3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_84cfad65-e9e9-42ad-a55f-74041d263b91" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d079def7-0405-48e0-8ace-dbe1d5aa0fbb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6de112b6-0fe8-473a-aab2-5d359f847bfd" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d079def7-0405-48e0-8ace-dbe1d5aa0fbb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_178eca06-47e6-46e1-9ff9-3d8490994aa9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d079def7-0405-48e0-8ace-dbe1d5aa0fbb" xlink:to="loc_us-gaap_AwardTypeAxis_178eca06-47e6-46e1-9ff9-3d8490994aa9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_178eca06-47e6-46e1-9ff9-3d8490994aa9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_178eca06-47e6-46e1-9ff9-3d8490994aa9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_178eca06-47e6-46e1-9ff9-3d8490994aa9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7c2fc2b8-793b-4970-93e2-66234f423e10" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_178eca06-47e6-46e1-9ff9-3d8490994aa9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7c2fc2b8-793b-4970-93e2-66234f423e10" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_TotalShareholderReturnMember_0165ea66-e51b-40b1-8667-71dde00a8e07" xlink:href="aciw-20230930.xsd#aciw_TotalShareholderReturnMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7c2fc2b8-793b-4970-93e2-66234f423e10" xlink:to="loc_aciw_TotalShareholderReturnMember_0165ea66-e51b-40b1-8667-71dde00a8e07" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.aciworldwide.com/role/StockBasedCompensationPlansScheduleofGrantDateFairValueWeightedAverageAssumptionsTSRsDetails" xlink:type="simple" xlink:href="aciw-20230930.xsd#StockBasedCompensationPlansScheduleofGrantDateFairValueWeightedAverageAssumptionsTSRsDetails"/>
  <link:definitionLink xlink:role="http://www.aciworldwide.com/role/StockBasedCompensationPlansScheduleofGrantDateFairValueWeightedAverageAssumptionsTSRsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8f8f02d2-1213-4d2f-a1f4-9dfccbed1276" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_ed2e57ac-3ac9-4a47-b958-5892b2823de5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8f8f02d2-1213-4d2f-a1f4-9dfccbed1276" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_ed2e57ac-3ac9-4a47-b958-5892b2823de5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_3aec8041-a98d-4b34-9fc9-d4582153db04" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8f8f02d2-1213-4d2f-a1f4-9dfccbed1276" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_3aec8041-a98d-4b34-9fc9-d4582153db04" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate_627eeb23-6a7e-41d0-a503-382d65bb7eff" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8f8f02d2-1213-4d2f-a1f4-9dfccbed1276" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate_627eeb23-6a7e-41d0-a503-382d65bb7eff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_3a0512ed-6f35-444e-8e22-3590ce00825c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8f8f02d2-1213-4d2f-a1f4-9dfccbed1276" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_3a0512ed-6f35-444e-8e22-3590ce00825c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_51a822cb-5124-4499-8261-d74232b973a4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8f8f02d2-1213-4d2f-a1f4-9dfccbed1276" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_51a822cb-5124-4499-8261-d74232b973a4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_edf89ad5-9386-4dce-a315-8b9c28eb0aaf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_51a822cb-5124-4499-8261-d74232b973a4" xlink:to="loc_us-gaap_AwardTypeAxis_edf89ad5-9386-4dce-a315-8b9c28eb0aaf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_edf89ad5-9386-4dce-a315-8b9c28eb0aaf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_edf89ad5-9386-4dce-a315-8b9c28eb0aaf" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_edf89ad5-9386-4dce-a315-8b9c28eb0aaf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a027fe82-6ea8-487a-adcb-003fdfc6c483" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_edf89ad5-9386-4dce-a315-8b9c28eb0aaf" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a027fe82-6ea8-487a-adcb-003fdfc6c483" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_TotalShareholderReturnMember_6648040e-1fc2-4d70-8f4f-ed7e0e85d19d" xlink:href="aciw-20230930.xsd#aciw_TotalShareholderReturnMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a027fe82-6ea8-487a-adcb-003fdfc6c483" xlink:to="loc_aciw_TotalShareholderReturnMember_6648040e-1fc2-4d70-8f4f-ed7e0e85d19d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueAxis_a11b0e7e-105d-4514-a768-c598d84a7127" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ValuationTechniqueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_51a822cb-5124-4499-8261-d74232b973a4" xlink:to="loc_us-gaap_ValuationTechniqueAxis_a11b0e7e-105d-4514-a768-c598d84a7127" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_a11b0e7e-105d-4514-a768-c598d84a7127_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationTechniqueAxis_a11b0e7e-105d-4514-a768-c598d84a7127" xlink:to="loc_us-gaap_ValuationTechniqueDomain_a11b0e7e-105d-4514-a768-c598d84a7127_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_2cb7b304-31bf-4562-a358-02373230768d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationTechniqueAxis_a11b0e7e-105d-4514-a768-c598d84a7127" xlink:to="loc_us-gaap_ValuationTechniqueDomain_2cb7b304-31bf-4562-a358-02373230768d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_MonteCarloSimulationValuationModelMember_59b78828-ea1c-4612-a0ec-0f6cb9cf3cb6" xlink:href="aciw-20230930.xsd#aciw_MonteCarloSimulationValuationModelMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_2cb7b304-31bf-4562-a358-02373230768d" xlink:to="loc_aciw_MonteCarloSimulationValuationModelMember_59b78828-ea1c-4612-a0ec-0f6cb9cf3cb6" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.aciworldwide.com/role/StockBasedCompensationPlansScheduleofNonvestedRestrictedShareUnitAwardsRSUsDetails" xlink:type="simple" xlink:href="aciw-20230930.xsd#StockBasedCompensationPlansScheduleofNonvestedRestrictedShareUnitAwardsRSUsDetails"/>
  <link:definitionLink xlink:role="http://www.aciworldwide.com/role/StockBasedCompensationPlansScheduleofNonvestedRestrictedShareUnitAwardsRSUsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b87466d9-ec0c-4258-b50e-4298cc2c65a9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_bf7a3100-706d-4ae8-954f-60b3d8e7519a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b87466d9-ec0c-4258-b50e-4298cc2c65a9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_bf7a3100-706d-4ae8-954f-60b3d8e7519a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_f76616c8-ffc8-4450-81c1-d7dd7d936362" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_bf7a3100-706d-4ae8-954f-60b3d8e7519a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_f76616c8-ffc8-4450-81c1-d7dd7d936362" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_4bb218e1-c108-49c5-8a01-687a1d4983c2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_bf7a3100-706d-4ae8-954f-60b3d8e7519a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_4bb218e1-c108-49c5-8a01-687a1d4983c2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_1bb9e6b1-2631-462e-bae3-9c79ef73e91b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_bf7a3100-706d-4ae8-954f-60b3d8e7519a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_1bb9e6b1-2631-462e-bae3-9c79ef73e91b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_c108af30-a87c-48e6-8d0a-252097bfbc7f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_bf7a3100-706d-4ae8-954f-60b3d8e7519a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_c108af30-a87c-48e6-8d0a-252097bfbc7f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_47b5ecb9-1daf-44e6-be01-63424a945ad7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_150a7d2d-3ed3-4fcc-9da2-b706f642b3e4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b87466d9-ec0c-4258-b50e-4298cc2c65a9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_150a7d2d-3ed3-4fcc-9da2-b706f642b3e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_b16d5c08-2158-418b-a077-17b3db1f5419" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_150a7d2d-3ed3-4fcc-9da2-b706f642b3e4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_b16d5c08-2158-418b-a077-17b3db1f5419" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_f061270c-9a03-4172-bdc3-e92b8d58b289" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_150a7d2d-3ed3-4fcc-9da2-b706f642b3e4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_f061270c-9a03-4172-bdc3-e92b8d58b289" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_c28a5734-8e6a-4af5-b5d7-61d96c3a4d1e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_150a7d2d-3ed3-4fcc-9da2-b706f642b3e4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_c28a5734-8e6a-4af5-b5d7-61d96c3a4d1e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_4350e2ca-a4a6-40e8-9c48-3b9484c584b3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_150a7d2d-3ed3-4fcc-9da2-b706f642b3e4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_4350e2ca-a4a6-40e8-9c48-3b9484c584b3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_083d3f64-4304-4da4-9c6d-6a6cf80188ea" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_2a7a6c90-22be-4a6b-bb0a-5065dd49afba" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b87466d9-ec0c-4258-b50e-4298cc2c65a9" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_2a7a6c90-22be-4a6b-bb0a-5065dd49afba" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_c35a163d-6f3d-4daa-8000-2d55da28047d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_2a7a6c90-22be-4a6b-bb0a-5065dd49afba" xlink:to="loc_us-gaap_AwardTypeAxis_c35a163d-6f3d-4daa-8000-2d55da28047d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c35a163d-6f3d-4daa-8000-2d55da28047d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_c35a163d-6f3d-4daa-8000-2d55da28047d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c35a163d-6f3d-4daa-8000-2d55da28047d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_8d5cfd71-582a-42c3-97e4-bf17d332dba9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_c35a163d-6f3d-4daa-8000-2d55da28047d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_8d5cfd71-582a-42c3-97e4-bf17d332dba9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_3ab9ef78-eb69-432c-8add-6dbdc06e1769" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_8d5cfd71-582a-42c3-97e4-bf17d332dba9" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_3ab9ef78-eb69-432c-8add-6dbdc06e1769" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.aciworldwide.com/role/SegmentInformationScheduleofReportableSegmentDetails" xlink:type="simple" xlink:href="aciw-20230930.xsd#SegmentInformationScheduleofReportableSegmentDetails"/>
  <link:definitionLink xlink:role="http://www.aciworldwide.com/role/SegmentInformationScheduleofReportableSegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_c83f6834-a3d6-4b2d-91b6-d22f9f030932" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_688f9cac-6da9-4f7c-b7a4-89a89aab624f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_c83f6834-a3d6-4b2d-91b6-d22f9f030932" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_688f9cac-6da9-4f7c-b7a4-89a89aab624f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_SegmentAdjustedEBITDA_873448f8-9dd9-4cd0-b612-bf97dc4993e4" xlink:href="aciw-20230930.xsd#aciw_SegmentAdjustedEBITDA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_c83f6834-a3d6-4b2d-91b6-d22f9f030932" xlink:to="loc_aciw_SegmentAdjustedEBITDA_873448f8-9dd9-4cd0-b612-bf97dc4993e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_e42126ba-148a-432d-a8a8-7087af7b75d4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_c83f6834-a3d6-4b2d-91b6-d22f9f030932" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_e42126ba-148a-432d-a8a8-7087af7b75d4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_5d2765c3-b01b-433a-8c9b-ed400892b599" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_c83f6834-a3d6-4b2d-91b6-d22f9f030932" xlink:to="loc_us-gaap_ShareBasedCompensation_5d2765c3-b01b-433a-8c9b-ed400892b599" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_CorporateAndUnallocatedIncomeExpense_66571b88-1bdb-46aa-af56-34fdbffa0aec" xlink:href="aciw-20230930.xsd#aciw_CorporateAndUnallocatedIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_c83f6834-a3d6-4b2d-91b6-d22f9f030932" xlink:to="loc_aciw_CorporateAndUnallocatedIncomeExpense_66571b88-1bdb-46aa-af56-34fdbffa0aec" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNet_f8a64536-5b16-4318-b439-bbe61dbccb16" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InterestIncomeExpenseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_c83f6834-a3d6-4b2d-91b6-d22f9f030932" xlink:to="loc_us-gaap_InterestIncomeExpenseNet_f8a64536-5b16-4318-b439-bbe61dbccb16" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_7a1bd2d6-3447-425b-afba-f5b101c342ba" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_c83f6834-a3d6-4b2d-91b6-d22f9f030932" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_7a1bd2d6-3447-425b-afba-f5b101c342ba" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_b5d6b830-79f8-4606-a59c-6ce8fccb7dfc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_c83f6834-a3d6-4b2d-91b6-d22f9f030932" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_b5d6b830-79f8-4606-a59c-6ce8fccb7dfc" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_bdd7565e-82a5-4d82-acbc-7b5c60ca692b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_c83f6834-a3d6-4b2d-91b6-d22f9f030932" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_bdd7565e-82a5-4d82-acbc-7b5c60ca692b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_28d81436-b993-4e41-9559-8f12635b9edf" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_bdd7565e-82a5-4d82-acbc-7b5c60ca692b" xlink:to="loc_srt_ConsolidationItemsAxis_28d81436-b993-4e41-9559-8f12635b9edf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_28d81436-b993-4e41-9559-8f12635b9edf_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_28d81436-b993-4e41-9559-8f12635b9edf" xlink:to="loc_srt_ConsolidationItemsDomain_28d81436-b993-4e41-9559-8f12635b9edf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_8935deaf-0eae-494d-86b6-3395f7f49fb8" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_28d81436-b993-4e41-9559-8f12635b9edf" xlink:to="loc_srt_ConsolidationItemsDomain_8935deaf-0eae-494d-86b6-3395f7f49fb8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_a7ab6655-b1f7-4688-9303-3bc405e20310" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_8935deaf-0eae-494d-86b6-3395f7f49fb8" xlink:to="loc_us-gaap_OperatingSegmentsMember_a7ab6655-b1f7-4688-9303-3bc405e20310" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_0c1d732a-51d9-4406-a813-9e4a803b5a82" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_bdd7565e-82a5-4d82-acbc-7b5c60ca692b" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_0c1d732a-51d9-4406-a813-9e4a803b5a82" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_0c1d732a-51d9-4406-a813-9e4a803b5a82_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_0c1d732a-51d9-4406-a813-9e4a803b5a82" xlink:to="loc_us-gaap_SegmentDomain_0c1d732a-51d9-4406-a813-9e4a803b5a82_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_9fd6367e-ce3c-4fdc-bf53-1da404283a87" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_0c1d732a-51d9-4406-a813-9e4a803b5a82" xlink:to="loc_us-gaap_SegmentDomain_9fd6367e-ce3c-4fdc-bf53-1da404283a87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_BanksMember_bb418e0a-50cc-4359-98b1-4b7a0f1c7e48" xlink:href="aciw-20230930.xsd#aciw_BanksMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_9fd6367e-ce3c-4fdc-bf53-1da404283a87" xlink:to="loc_aciw_BanksMember_bb418e0a-50cc-4359-98b1-4b7a0f1c7e48" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_MerchantsMember_8dd40a08-0965-48be-997c-98232c7c0793" xlink:href="aciw-20230930.xsd#aciw_MerchantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_9fd6367e-ce3c-4fdc-bf53-1da404283a87" xlink:to="loc_aciw_MerchantsMember_8dd40a08-0965-48be-997c-98232c7c0793" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_BillersMember_b6648b2b-c580-405b-8c65-ea74bdb7708b" xlink:href="aciw-20230930.xsd#aciw_BillersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_9fd6367e-ce3c-4fdc-bf53-1da404283a87" xlink:to="loc_aciw_BillersMember_b6648b2b-c580-405b-8c65-ea74bdb7708b" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.aciworldwide.com/role/SegmentInformationScheduleofRevenuesbyPrimarySolutionCategoriesGeographicalLocationandLongLivedAssetsDetails" xlink:type="simple" xlink:href="aciw-20230930.xsd#SegmentInformationScheduleofRevenuesbyPrimarySolutionCategoriesGeographicalLocationandLongLivedAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.aciworldwide.com/role/SegmentInformationScheduleofRevenuesbyPrimarySolutionCategoriesGeographicalLocationandLongLivedAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_0ebe47b6-30e1-4a45-9a5a-704955488a4e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_783679e0-589b-43dc-b7f8-c8e74e1741f8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_0ebe47b6-30e1-4a45-9a5a-704955488a4e" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_783679e0-589b-43dc-b7f8-c8e74e1741f8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeographicAreasLongLivedAssetsAbstract_83b78a8f-6ef6-42dd-bc78-040853ff2d27" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GeographicAreasLongLivedAssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_0ebe47b6-30e1-4a45-9a5a-704955488a4e" xlink:to="loc_us-gaap_GeographicAreasLongLivedAssetsAbstract_83b78a8f-6ef6-42dd-bc78-040853ff2d27" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncurrentAssets_cdeb68bf-13b2-491d-81d1-3e539c35ac40" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GeographicAreasLongLivedAssetsAbstract_83b78a8f-6ef6-42dd-bc78-040853ff2d27" xlink:to="loc_us-gaap_NoncurrentAssets_cdeb68bf-13b2-491d-81d1-3e539c35ac40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_c1553822-5031-4bb4-8eca-995bf67f565a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_0ebe47b6-30e1-4a45-9a5a-704955488a4e" xlink:to="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_c1553822-5031-4bb4-8eca-995bf67f565a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_877c3908-fe09-4b00-8787-1986795f8369" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_c1553822-5031-4bb4-8eca-995bf67f565a" xlink:to="loc_srt_ConsolidationItemsAxis_877c3908-fe09-4b00-8787-1986795f8369" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_877c3908-fe09-4b00-8787-1986795f8369_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_877c3908-fe09-4b00-8787-1986795f8369" xlink:to="loc_srt_ConsolidationItemsDomain_877c3908-fe09-4b00-8787-1986795f8369_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_69e8ac43-cc50-4172-8a65-31794bac1980" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_877c3908-fe09-4b00-8787-1986795f8369" xlink:to="loc_srt_ConsolidationItemsDomain_69e8ac43-cc50-4172-8a65-31794bac1980" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_d5db830a-8a08-419b-a43d-5ef363c64246" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_69e8ac43-cc50-4172-8a65-31794bac1980" xlink:to="loc_us-gaap_OperatingSegmentsMember_d5db830a-8a08-419b-a43d-5ef363c64246" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_3d77e18f-54d9-47e8-a8ae-5f527cb0d781" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_c1553822-5031-4bb4-8eca-995bf67f565a" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_3d77e18f-54d9-47e8-a8ae-5f527cb0d781" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_3d77e18f-54d9-47e8-a8ae-5f527cb0d781_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_3d77e18f-54d9-47e8-a8ae-5f527cb0d781" xlink:to="loc_us-gaap_SegmentDomain_3d77e18f-54d9-47e8-a8ae-5f527cb0d781_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_8824c6f7-c8f7-4eed-bb96-82615542cc51" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_3d77e18f-54d9-47e8-a8ae-5f527cb0d781" xlink:to="loc_us-gaap_SegmentDomain_8824c6f7-c8f7-4eed-bb96-82615542cc51" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_BanksMember_65f90260-bccb-4197-a8eb-f8bb64b21986" xlink:href="aciw-20230930.xsd#aciw_BanksMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_8824c6f7-c8f7-4eed-bb96-82615542cc51" xlink:to="loc_aciw_BanksMember_65f90260-bccb-4197-a8eb-f8bb64b21986" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_MerchantsMember_660697e0-9ba4-4df7-816a-64cccbac5b25" xlink:href="aciw-20230930.xsd#aciw_MerchantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_8824c6f7-c8f7-4eed-bb96-82615542cc51" xlink:to="loc_aciw_MerchantsMember_660697e0-9ba4-4df7-816a-64cccbac5b25" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_BillersMember_3e91f2bd-b765-4425-aec5-dea265e1350b" xlink:href="aciw-20230930.xsd#aciw_BillersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_8824c6f7-c8f7-4eed-bb96-82615542cc51" xlink:to="loc_aciw_BillersMember_3e91f2bd-b765-4425-aec5-dea265e1350b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_ec45c55c-9b03-4739-b019-ef83f63b5ab4" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_c1553822-5031-4bb4-8eca-995bf67f565a" xlink:to="loc_srt_ProductOrServiceAxis_ec45c55c-9b03-4739-b019-ef83f63b5ab4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_ec45c55c-9b03-4739-b019-ef83f63b5ab4_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_ec45c55c-9b03-4739-b019-ef83f63b5ab4" xlink:to="loc_srt_ProductsAndServicesDomain_ec45c55c-9b03-4739-b019-ef83f63b5ab4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_8fb952a3-7bda-41e2-baef-1910d075a234" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_ec45c55c-9b03-4739-b019-ef83f63b5ab4" xlink:to="loc_srt_ProductsAndServicesDomain_8fb952a3-7bda-41e2-baef-1910d075a234" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_BillerPaymentsMember_8036a1b5-2701-4e6a-8a36-0cfcfccfb40b" xlink:href="aciw-20230930.xsd#aciw_BillerPaymentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_8fb952a3-7bda-41e2-baef-1910d075a234" xlink:to="loc_aciw_BillerPaymentsMember_8036a1b5-2701-4e6a-8a36-0cfcfccfb40b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_DigitalBusinessBankingMember_ca72fbce-f17a-4a4f-a3fe-309558fdc867" xlink:href="aciw-20230930.xsd#aciw_DigitalBusinessBankingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_8fb952a3-7bda-41e2-baef-1910d075a234" xlink:to="loc_aciw_DigitalBusinessBankingMember_ca72fbce-f17a-4a4f-a3fe-309558fdc867" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_MerchantPaymentsMember_f53ed0e4-86ef-43db-aac6-6ed834b50b2c" xlink:href="aciw-20230930.xsd#aciw_MerchantPaymentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_8fb952a3-7bda-41e2-baef-1910d075a234" xlink:to="loc_aciw_MerchantPaymentsMember_f53ed0e4-86ef-43db-aac6-6ed834b50b2c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_FraudManagementMember_eb6f52c2-507e-4fe8-af84-b0fe23c099e5" xlink:href="aciw-20230930.xsd#aciw_FraudManagementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_8fb952a3-7bda-41e2-baef-1910d075a234" xlink:to="loc_aciw_FraudManagementMember_eb6f52c2-507e-4fe8-af84-b0fe23c099e5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_RealTimePaymentsMember_ccd84055-49df-4cca-9d69-d404bcd8d5d0" xlink:href="aciw-20230930.xsd#aciw_RealTimePaymentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_8fb952a3-7bda-41e2-baef-1910d075a234" xlink:to="loc_aciw_RealTimePaymentsMember_ccd84055-49df-4cca-9d69-d404bcd8d5d0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_IssuingAndAcquiringMember_84530d25-4694-40f3-acfa-46011411f4d6" xlink:href="aciw-20230930.xsd#aciw_IssuingAndAcquiringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_8fb952a3-7bda-41e2-baef-1910d075a234" xlink:to="loc_aciw_IssuingAndAcquiringMember_84530d25-4694-40f3-acfa-46011411f4d6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_SoftwareAndPlatformServiceMember_8a8afd60-94d7-4be2-9cff-ffeb8d83603d" xlink:href="aciw-20230930.xsd#aciw_SoftwareAndPlatformServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_8fb952a3-7bda-41e2-baef-1910d075a234" xlink:to="loc_aciw_SoftwareAndPlatformServiceMember_8a8afd60-94d7-4be2-9cff-ffeb8d83603d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LicenseMember_359ab4e1-a37e-4a9e-9452-8dcb05661993" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_8fb952a3-7bda-41e2-baef-1910d075a234" xlink:to="loc_us-gaap_LicenseMember_359ab4e1-a37e-4a9e-9452-8dcb05661993" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaintenanceMember_8ff8176b-8bad-4bec-9883-5bcbddbcbba1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MaintenanceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_8fb952a3-7bda-41e2-baef-1910d075a234" xlink:to="loc_us-gaap_MaintenanceMember_8ff8176b-8bad-4bec-9883-5bcbddbcbba1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceMember_6d02529c-c281-43f4-b64e-9e4a6b7cc214" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_8fb952a3-7bda-41e2-baef-1910d075a234" xlink:to="loc_us-gaap_ServiceMember_6d02529c-c281-43f4-b64e-9e4a6b7cc214" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_d747de9e-9513-4dc1-b7d8-2fa6d56f3b5c" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_c1553822-5031-4bb4-8eca-995bf67f565a" xlink:to="loc_srt_StatementGeographicalAxis_d747de9e-9513-4dc1-b7d8-2fa6d56f3b5c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_d747de9e-9513-4dc1-b7d8-2fa6d56f3b5c_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_d747de9e-9513-4dc1-b7d8-2fa6d56f3b5c" xlink:to="loc_srt_SegmentGeographicalDomain_d747de9e-9513-4dc1-b7d8-2fa6d56f3b5c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_f625ac8e-92d5-409f-a1af-0c0e78a588c3" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_d747de9e-9513-4dc1-b7d8-2fa6d56f3b5c" xlink:to="loc_srt_SegmentGeographicalDomain_f625ac8e-92d5-409f-a1af-0c0e78a588c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_79fc0729-8d50-4e02-884d-6d2b0fff375e" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_f625ac8e-92d5-409f-a1af-0c0e78a588c3" xlink:to="loc_country_US_79fc0729-8d50-4e02-884d-6d2b0fff375e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonUsMember_ad263a7f-6940-4717-9988-cca356060c8c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NonUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_f625ac8e-92d5-409f-a1af-0c0e78a588c3" xlink:to="loc_us-gaap_NonUsMember_ad263a7f-6940-4717-9988-cca356060c8c" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.aciworldwide.com/role/IncomeTaxesDetails" xlink:type="simple" xlink:href="aciw-20230930.xsd#IncomeTaxesDetails"/>
  <link:definitionLink xlink:role="http://www.aciworldwide.com/role/IncomeTaxesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxContingencyLineItems_0ee77359-ec18-4d49-9161-474daf5acbd4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxContingencyLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_dbaf71a8-3bf6-4301-8888-b11d8a26d754" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_0ee77359-ec18-4d49-9161-474daf5acbd4" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_dbaf71a8-3bf6-4301-8888-b11d8a26d754" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign_64fee8e6-dc93-4065-aa58-2be43404c76c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_0ee77359-ec18-4d49-9161-474daf5acbd4" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign_64fee8e6-dc93-4065-aa58-2be43404c76c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_UnrecognizedTaxBenefitsIncreaseResultingFromPendingRegulationUpdatesWithTaxingAuthorities_e4bffaa7-3572-41d6-8b19-483d7cb48e3e" xlink:href="aciw-20230930.xsd#aciw_UnrecognizedTaxBenefitsIncreaseResultingFromPendingRegulationUpdatesWithTaxingAuthorities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_0ee77359-ec18-4d49-9161-474daf5acbd4" xlink:to="loc_aciw_UnrecognizedTaxBenefitsIncreaseResultingFromPendingRegulationUpdatesWithTaxingAuthorities_e4bffaa7-3572-41d6-8b19-483d7cb48e3e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefits_a928443f-87fd-4b75-b52b-cc8a9d51863c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_UnrecognizedTaxBenefits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_0ee77359-ec18-4d49-9161-474daf5acbd4" xlink:to="loc_us-gaap_UnrecognizedTaxBenefits_a928443f-87fd-4b75-b52b-cc8a9d51863c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued_4c63c142-3ae3-4e64-898a-40b533a77efb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_0ee77359-ec18-4d49-9161-474daf5acbd4" xlink:to="loc_us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued_4c63c142-3ae3-4e64-898a-40b533a77efb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DecreaseInUnrecognizedTaxBenefitsIsReasonablyPossible_9e7266e0-5246-41b1-b3fe-a06fa5b3fd4f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DecreaseInUnrecognizedTaxBenefitsIsReasonablyPossible"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_0ee77359-ec18-4d49-9161-474daf5acbd4" xlink:to="loc_us-gaap_DecreaseInUnrecognizedTaxBenefitsIsReasonablyPossible_9e7266e0-5246-41b1-b3fe-a06fa5b3fd4f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxContingencyTable_33bb72b8-ac87-424f-9114-a9f804b4c3ec" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxContingencyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_0ee77359-ec18-4d49-9161-474daf5acbd4" xlink:to="loc_us-gaap_IncomeTaxContingencyTable_33bb72b8-ac87-424f-9114-a9f804b4c3ec" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityNameAxis_e47cb496-dbfc-4cce-b3c3-fc4745d70a79" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxAuthorityNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeTaxContingencyTable_33bb72b8-ac87-424f-9114-a9f804b4c3ec" xlink:to="loc_us-gaap_IncomeTaxAuthorityNameAxis_e47cb496-dbfc-4cce-b3c3-fc4745d70a79" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityNameDomain_e47cb496-dbfc-4cce-b3c3-fc4745d70a79_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxAuthorityNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityNameAxis_e47cb496-dbfc-4cce-b3c3-fc4745d70a79" xlink:to="loc_us-gaap_IncomeTaxAuthorityNameDomain_e47cb496-dbfc-4cce-b3c3-fc4745d70a79_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityNameDomain_6a2d6c34-12bc-46b4-97b3-d9638e44e0fb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxAuthorityNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityNameAxis_e47cb496-dbfc-4cce-b3c3-fc4745d70a79" xlink:to="loc_us-gaap_IncomeTaxAuthorityNameDomain_6a2d6c34-12bc-46b4-97b3-d9638e44e0fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalRevenueServiceIRSMember_74c955b0-6553-4f70-acc2-eef740163ff3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InternalRevenueServiceIRSMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityNameDomain_6a2d6c34-12bc-46b4-97b3-d9638e44e0fb" xlink:to="loc_us-gaap_InternalRevenueServiceIRSMember_74c955b0-6553-4f70-acc2-eef740163ff3" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.aciworldwide.com/role/CommitmentsandContingenciesDetails" xlink:type="simple" xlink:href="aciw-20230930.xsd#CommitmentsandContingenciesDetails"/>
  <link:definitionLink xlink:role="http://www.aciworldwide.com/role/CommitmentsandContingenciesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_d66b017e-3c79-4b6f-bd9d-57aeb316040a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyPendingClaimsNumber_36c5ad72-81eb-4e7a-a32c-7e9620d02869" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LossContingencyPendingClaimsNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_d66b017e-3c79-4b6f-bd9d-57aeb316040a" xlink:to="loc_us-gaap_LossContingencyPendingClaimsNumber_36c5ad72-81eb-4e7a-a32c-7e9620d02869" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementAmountAwardedToOtherParty_1728002d-cf63-47ef-84b3-39b9be86b030" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LitigationSettlementAmountAwardedToOtherParty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_d66b017e-3c79-4b6f-bd9d-57aeb316040a" xlink:to="loc_us-gaap_LitigationSettlementAmountAwardedToOtherParty_1728002d-cf63-47ef-84b3-39b9be86b030" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_LitigationSettlementContingentConsiderationLiability_db71c2de-5464-42ef-b062-8ea7fa4ddbdf" xlink:href="aciw-20230930.xsd#aciw_LitigationSettlementContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_d66b017e-3c79-4b6f-bd9d-57aeb316040a" xlink:to="loc_aciw_LitigationSettlementContingentConsiderationLiability_db71c2de-5464-42ef-b062-8ea7fa4ddbdf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_5ab665b7-91fe-4d75-80f0-7a19fa877307" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_d66b017e-3c79-4b6f-bd9d-57aeb316040a" xlink:to="loc_us-gaap_LossContingenciesTable_5ab665b7-91fe-4d75-80f0-7a19fa877307" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseAxis_0022f0f9-ce4f-49ef-883a-79de044bbd24" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_LitigationCaseAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_5ab665b7-91fe-4d75-80f0-7a19fa877307" xlink:to="loc_srt_LitigationCaseAxis_0022f0f9-ce4f-49ef-883a-79de044bbd24" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_0022f0f9-ce4f-49ef-883a-79de044bbd24_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_LitigationCaseAxis_0022f0f9-ce4f-49ef-883a-79de044bbd24" xlink:to="loc_srt_LitigationCaseTypeDomain_0022f0f9-ce4f-49ef-883a-79de044bbd24_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_0fd4c3f2-9c88-4151-a083-dcbae4869e83" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_LitigationCaseAxis_0022f0f9-ce4f-49ef-883a-79de044bbd24" xlink:to="loc_srt_LitigationCaseTypeDomain_0fd4c3f2-9c88-4151-a083-dcbae4869e83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_ACHFileTransmissionMember_46eb51d6-48e0-4981-b83f-39293d569d81" xlink:href="aciw-20230930.xsd#aciw_ACHFileTransmissionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_LitigationCaseTypeDomain_0fd4c3f2-9c88-4151-a083-dcbae4869e83" xlink:to="loc_aciw_ACHFileTransmissionMember_46eb51d6-48e0-4981-b83f-39293d569d81" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationStatusAxis_27b0c34e-03b9-4039-b414-da208a348044" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LitigationStatusAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_5ab665b7-91fe-4d75-80f0-7a19fa877307" xlink:to="loc_us-gaap_LitigationStatusAxis_27b0c34e-03b9-4039-b414-da208a348044" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationStatusDomain_27b0c34e-03b9-4039-b414-da208a348044_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LitigationStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LitigationStatusAxis_27b0c34e-03b9-4039-b414-da208a348044" xlink:to="loc_us-gaap_LitigationStatusDomain_27b0c34e-03b9-4039-b414-da208a348044_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationStatusDomain_53ff692d-308d-47ed-ba69-543ac8e3088a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LitigationStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LitigationStatusAxis_27b0c34e-03b9-4039-b414-da208a348044" xlink:to="loc_us-gaap_LitigationStatusDomain_53ff692d-308d-47ed-ba69-543ac8e3088a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SettledLitigationMember_5e34af7c-097e-44d4-9dba-70371999d13f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SettledLitigationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LitigationStatusDomain_53ff692d-308d-47ed-ba69-543ac8e3088a" xlink:to="loc_us-gaap_SettledLitigationMember_5e34af7c-097e-44d4-9dba-70371999d13f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_afd406f1-ad69-48bd-9450-025991e598af" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_5ab665b7-91fe-4d75-80f0-7a19fa877307" xlink:to="loc_srt_CounterpartyNameAxis_afd406f1-ad69-48bd-9450-025991e598af" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_afd406f1-ad69-48bd-9450-025991e598af_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_afd406f1-ad69-48bd-9450-025991e598af" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_afd406f1-ad69-48bd-9450-025991e598af_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_03306c79-9760-4e54-bff6-b2bd0f0f30c5" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_afd406f1-ad69-48bd-9450-025991e598af" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_03306c79-9760-4e54-bff6-b2bd0f0f30c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_USConsumerFinancialProtectionBureauAndStateAttorneysGeneralMember_697fecd2-1070-41b2-8608-59e348d959b0" xlink:href="aciw-20230930.xsd#aciw_USConsumerFinancialProtectionBureauAndStateAttorneysGeneralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_03306c79-9760-4e54-bff6-b2bd0f0f30c5" xlink:to="loc_aciw_USConsumerFinancialProtectionBureauAndStateAttorneysGeneralMember_697fecd2-1070-41b2-8608-59e348d959b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_StateMoneyTransmissionRegulatorsAndStateAttorneysGeneralMember_fa60e35e-e631-4737-a4c8-8297477f0f6d" xlink:href="aciw-20230930.xsd#aciw_StateMoneyTransmissionRegulatorsAndStateAttorneysGeneralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aciw_USConsumerFinancialProtectionBureauAndStateAttorneysGeneralMember_697fecd2-1070-41b2-8608-59e348d959b0" xlink:to="loc_aciw_StateMoneyTransmissionRegulatorsAndStateAttorneysGeneralMember_fa60e35e-e631-4737-a4c8-8297477f0f6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_84821d2a-d385-46c9-b7cb-a8033a6179ec" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_5ab665b7-91fe-4d75-80f0-7a19fa877307" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_84821d2a-d385-46c9-b7cb-a8033a6179ec" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_84821d2a-d385-46c9-b7cb-a8033a6179ec_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_84821d2a-d385-46c9-b7cb-a8033a6179ec" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_84821d2a-d385-46c9-b7cb-a8033a6179ec_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_14e203b1-8252-498c-a495-7021e7593245" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_84821d2a-d385-46c9-b7cb-a8033a6179ec" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_14e203b1-8252-498c-a495-7021e7593245" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_64d39fc1-352c-44de-b1d9-bbd7c9022158" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_14e203b1-8252-498c-a495-7021e7593245" xlink:to="loc_us-gaap_SubsequentEventMember_64d39fc1-352c-44de-b1d9-bbd7c9022158" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/AwardTypeOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2023/ecd-2023.xsd#AwardTypeOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/AwardTypeOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:loc xlink:type="locator" xlink:label="loc_aciw_TotalShareholderReturnMember_daf7e703-34ee-4757-960b-fe237055ef24" xlink:href="aciw-20230930.xsd#aciw_TotalShareholderReturnMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_aciw_TotalShareholderReturnMember_daf7e703-34ee-4757-960b-fe237055ef24" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember" xlink:type="arc" order="5"/>
  </link:definitionLink>
</link:linkbase>
