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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019fd7b0-f961-79f9-8fc1-3d3fd8c2614a,g:072b80d0-5862-441b-a0e4-9d20c6509b1b-->
<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.mirion.com/role/CoverPage" xlink:type="simple" xlink:href="mir-20260930.xsd#CoverPage"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/CoverPage" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_019fd7b0-fb2a-768c-a2e5-6877fd6bb5ca" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_DocumentInformationTable_019fd7b0-fb2a-768c-a2e5-6877fd6bb5ca" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7af1-bd7b-f4621bcbc90d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_019fd7b0-fb2a-768c-a2e5-6877fd6bb5ca" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7af1-bd7b-f4621bcbc90d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7af1-bd7b-f4621bcbc90d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7af1-bd7b-f4621bcbc90d" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7af1-bd7b-f4621bcbc90d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-77fc-acb1-2eb3f93c59f0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7af1-bd7b-f4621bcbc90d" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-77fc-acb1-2eb3f93c59f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019fd7b0-fb2a-796e-8598-b756620bb221" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-77fc-acb1-2eb3f93c59f0" xlink:to="loc_us-gaap_CommonClassAMember_019fd7b0-fb2a-796e-8598-b756620bb221" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019fd7b0-fb2a-7a38-92ea-f15ede5ae95a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-77fc-acb1-2eb3f93c59f0" xlink:to="loc_us-gaap_CommonClassBMember_019fd7b0-fb2a-7a38-92ea-f15ede5ae95a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019fd7b0-fb2a-7670-98b5-461ecfb3d4ad" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_DocumentType_019fd7b0-fb2a-7670-98b5-461ecfb3d4ad" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_019fd7b0-fb2a-7d60-a193-7d0f30abc3ae" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_DocumentQuarterlyReport_019fd7b0-fb2a-7d60-a193-7d0f30abc3ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019fd7b0-fb2a-7bbb-a908-ba340ada3a60" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_DocumentPeriodEndDate_019fd7b0-fb2a-7bbb-a908-ba340ada3a60" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_019fd7b0-fb2a-7f01-990f-22f597a5d04c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_DocumentTransitionReport_019fd7b0-fb2a-7f01-990f-22f597a5d04c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019fd7b0-fb2a-7278-aaf3-728f4ef8ef2a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_EntityFileNumber_019fd7b0-fb2a-7278-aaf3-728f4ef8ef2a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019fd7b0-fb2a-7fa0-baac-266fc10b8991" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_EntityRegistrantName_019fd7b0-fb2a-7fa0-baac-266fc10b8991" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019fd7b0-fb2a-7e67-9ca9-0195fae4b136" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019fd7b0-fb2a-7e67-9ca9-0195fae4b136" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019fd7b0-fb2a-7252-b312-758d30319451" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_EntityTaxIdentificationNumber_019fd7b0-fb2a-7252-b312-758d30319451" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019fd7b0-fb2a-7e11-bb4a-62c41e983039" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_EntityAddressAddressLine1_019fd7b0-fb2a-7e11-bb4a-62c41e983039" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019fd7b0-fb2a-776c-8474-6d698d6febb5" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_EntityAddressCityOrTown_019fd7b0-fb2a-776c-8474-6d698d6febb5" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019fd7b0-fb2a-7cc3-a4b8-50f2f7e2eb29" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_EntityAddressStateOrProvince_019fd7b0-fb2a-7cc3-a4b8-50f2f7e2eb29" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019fd7b0-fb2a-7ac1-a209-485702c3d60e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_EntityAddressPostalZipCode_019fd7b0-fb2a-7ac1-a209-485702c3d60e" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019fd7b0-fb2a-7ba7-bb5a-820d4e633138" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_CityAreaCode_019fd7b0-fb2a-7ba7-bb5a-820d4e633138" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019fd7b0-fb2a-7ba9-8c7d-678441c5fca5" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_LocalPhoneNumber_019fd7b0-fb2a-7ba9-8c7d-678441c5fca5" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019fd7b0-fb2a-7a31-af07-ab667f20d9fe" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_Security12bTitle_019fd7b0-fb2a-7a31-af07-ab667f20d9fe" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019fd7b0-fb2a-7156-bdba-742bb7d518b5" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_TradingSymbol_019fd7b0-fb2a-7156-bdba-742bb7d518b5" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019fd7b0-fb2a-77b4-925f-0418e5367670" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_SecurityExchangeName_019fd7b0-fb2a-77b4-925f-0418e5367670" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_019fd7b0-fb2a-7487-ab76-756d466ffb27" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_EntityCurrentReportingStatus_019fd7b0-fb2a-7487-ab76-756d466ffb27" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_019fd7b0-fb2a-72e6-a0a9-4947e7557c2b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_EntityInteractiveDataCurrent_019fd7b0-fb2a-72e6-a0a9-4947e7557c2b" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_019fd7b0-fb2a-7ac7-a08d-b32112bdba37" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_EntityFilerCategory_019fd7b0-fb2a-7ac7-a08d-b32112bdba37" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_019fd7b0-fb2a-7be7-abfa-8b215bf101b0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_EntitySmallBusiness_019fd7b0-fb2a-7be7-abfa-8b215bf101b0" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019fd7b0-fb2a-7d7a-b115-43bb0e70b158" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_EntityEmergingGrowthCompany_019fd7b0-fb2a-7d7a-b115-43bb0e70b158" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_019fd7b0-fb2a-7c47-9d55-aa5e1c5fb872" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_EntityShellCompany_019fd7b0-fb2a-7c47-9d55-aa5e1c5fb872" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_019fd7b0-fb2a-76a6-94d1-2e0355e4f28e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_019fd7b0-fb2a-76a6-94d1-2e0355e4f28e" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_019fd7b0-fb2a-7030-b7a0-d98d40117f00" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_DocumentFiscalPeriodFocus_019fd7b0-fb2a-7030-b7a0-d98d40117f00" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019fd7b0-fb2a-7dbb-95f7-5481b7dfa813" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_AmendmentFlag_019fd7b0-fb2a-7dbb-95f7-5481b7dfa813" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_019fd7b0-fb2a-7e43-930c-f3462ca6a5b3" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_DocumentFiscalYearFocus_019fd7b0-fb2a-7e43-930c-f3462ca6a5b3" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_019fd7b0-fb2a-7904-9933-79eeef3acfc0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_CurrentFiscalYearEndDate_019fd7b0-fb2a-7904-9933-79eeef3acfc0" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019fd7b0-fb2a-71de-9cfa-90b808381ef2" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019fd7b0-fb2a-7803-a155-74dc190df212" xlink:to="loc_dei_EntityCentralIndexKey_019fd7b0-fb2a-71de-9cfa-90b808381ef2" xlink:type="arc" order="28"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/CondensedConsolidatedBalanceSheets" xlink:type="simple" xlink:href="mir-20260930.xsd#CondensedConsolidatedBalanceSheets"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/CondensedConsolidatedBalanceSheets" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-77b2-b2b6-d6aebaa6fdad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019fd7b0-fb2a-73aa-99cb-d0440a1d0dc6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-77b2-b2b6-d6aebaa6fdad" xlink:to="loc_us-gaap_StatementTable_019fd7b0-fb2a-73aa-99cb-d0440a1d0dc6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-783b-b2bd-55d7e0caaa31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019fd7b0-fb2a-73aa-99cb-d0440a1d0dc6" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-783b-b2bd-55d7e0caaa31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-783b-b2bd-55d7e0caaa31_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-783b-b2bd-55d7e0caaa31" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-783b-b2bd-55d7e0caaa31_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7b21-a3a1-2bf1055d3abb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-783b-b2bd-55d7e0caaa31" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7b21-a3a1-2bf1055d3abb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019fd7b0-fb2a-7bf0-ac02-2be91e8c51a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7b21-a3a1-2bf1055d3abb" xlink:to="loc_us-gaap_CommonClassAMember_019fd7b0-fb2a-7bf0-ac02-2be91e8c51a8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019fd7b0-fb2a-7a7b-b1cf-4763493246de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7b21-a3a1-2bf1055d3abb" xlink:to="loc_us-gaap_CommonClassBMember_019fd7b0-fb2a-7a7b-b1cf-4763493246de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_019fd7b0-fb2a-7e3c-a3e6-f734a19881db" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-77b2-b2b6-d6aebaa6fdad" xlink:to="loc_us-gaap_AssetsAbstract_019fd7b0-fb2a-7e3c-a3e6-f734a19881db" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_019fd7b0-fb2a-7c10-b05a-656bb71b8f2a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd7b0-fb2a-7e3c-a3e6-f734a19881db" xlink:to="loc_us-gaap_AssetsCurrentAbstract_019fd7b0-fb2a-7c10-b05a-656bb71b8f2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019fd7b0-fb2a-7922-8d95-0abb9db08620" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019fd7b0-fb2a-7c10-b05a-656bb71b8f2a" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019fd7b0-fb2a-7922-8d95-0abb9db08620" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_019fd7b0-fb2a-78a1-8167-d573d9907f02" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019fd7b0-fb2a-7c10-b05a-656bb71b8f2a" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_019fd7b0-fb2a-78a1-8167-d573d9907f02" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNetCurrent_019fd7b0-fb2a-700c-aa03-6ecc5180be96" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerAssetNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019fd7b0-fb2a-7c10-b05a-656bb71b8f2a" xlink:to="loc_us-gaap_ContractWithCustomerAssetNetCurrent_019fd7b0-fb2a-700c-aa03-6ecc5180be96" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_019fd7b0-fb2a-70a4-8cb3-67344cdc23b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019fd7b0-fb2a-7c10-b05a-656bb71b8f2a" xlink:to="loc_us-gaap_InventoryNet_019fd7b0-fb2a-70a4-8cb3-67344cdc23b0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019fd7b0-fb2a-7c8f-8d46-122fd1b33300" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019fd7b0-fb2a-7c10-b05a-656bb71b8f2a" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019fd7b0-fb2a-7c8f-8d46-122fd1b33300" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_019fd7b0-fb2a-7f94-8259-6a77bbe3b876" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019fd7b0-fb2a-7c10-b05a-656bb71b8f2a" xlink:to="loc_us-gaap_AssetsCurrent_019fd7b0-fb2a-7f94-8259-6a77bbe3b876" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019fd7b0-fb2a-7164-9c18-a747f2052747" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd7b0-fb2a-7e3c-a3e6-f734a19881db" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019fd7b0-fb2a-7164-9c18-a747f2052747" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_019fd7b0-fb2a-7f54-85d9-026c66d8fc6c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd7b0-fb2a-7e3c-a3e6-f734a19881db" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_019fd7b0-fb2a-7f54-85d9-026c66d8fc6c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019fd7b0-fb2a-7f98-94ec-4263db3bc7f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd7b0-fb2a-7e3c-a3e6-f734a19881db" xlink:to="loc_us-gaap_Goodwill_019fd7b0-fb2a-7f98-94ec-4263db3bc7f7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019fd7b0-fb2a-792a-ad18-339b18874702" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd7b0-fb2a-7e3c-a3e6-f734a19881db" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019fd7b0-fb2a-792a-ad18-339b18874702" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_019fd7b0-fb2a-7db8-a9ae-34e52ab74497" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd7b0-fb2a-7e3c-a3e6-f734a19881db" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_019fd7b0-fb2a-7db8-a9ae-34e52ab74497" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019fd7b0-fb2a-7faf-bbe3-1c820eb8ffb8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd7b0-fb2a-7e3c-a3e6-f734a19881db" xlink:to="loc_us-gaap_Assets_019fd7b0-fb2a-7faf-bbe3-1c820eb8ffb8" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019fd7b0-fb2a-7967-ac07-2af256352082" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-77b2-b2b6-d6aebaa6fdad" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019fd7b0-fb2a-7967-ac07-2af256352082" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_019fd7b0-fb2a-7d8d-be8e-fe1fe06c3693" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019fd7b0-fb2a-7967-ac07-2af256352082" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_019fd7b0-fb2a-7d8d-be8e-fe1fe06c3693" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_019fd7b0-fb2a-7ee9-b691-7a8a7159735f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019fd7b0-fb2a-7d8d-be8e-fe1fe06c3693" xlink:to="loc_us-gaap_AccountsPayableCurrent_019fd7b0-fb2a-7ee9-b691-7a8a7159735f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredRevenueCurrent_019fd7b0-fb2a-7f1e-9ed8-4ba2d92d2cde" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredRevenueCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019fd7b0-fb2a-7d8d-be8e-fe1fe06c3693" xlink:to="loc_us-gaap_DeferredRevenueCurrent_019fd7b0-fb2a-7f1e-9ed8-4ba2d92d2cde" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_019fd7b0-fb2a-779f-a16b-b1b7327b30b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019fd7b0-fb2a-7d8d-be8e-fe1fe06c3693" xlink:to="loc_us-gaap_LongTermDebtCurrent_019fd7b0-fb2a-779f-a16b-b1b7327b30b8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_019fd7b0-fb2a-7e2d-91f8-cf27a3e01194" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019fd7b0-fb2a-7d8d-be8e-fe1fe06c3693" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_019fd7b0-fb2a-7e2d-91f8-cf27a3e01194" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilitiesCurrent_019fd7b0-fb2a-745f-a4ae-a5c482e14b5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019fd7b0-fb2a-7d8d-be8e-fe1fe06c3693" xlink:to="loc_us-gaap_DerivativeLiabilitiesCurrent_019fd7b0-fb2a-745f-a4ae-a5c482e14b5b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesAndOtherLiabilities_019fd7b0-fb2a-7674-a65f-3554e8ddb2ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccruedLiabilitiesAndOtherLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019fd7b0-fb2a-7d8d-be8e-fe1fe06c3693" xlink:to="loc_us-gaap_AccruedLiabilitiesAndOtherLiabilities_019fd7b0-fb2a-7674-a65f-3554e8ddb2ab" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_019fd7b0-fb2a-7c45-a8eb-d78c37c9d87c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019fd7b0-fb2a-7d8d-be8e-fe1fe06c3693" xlink:to="loc_us-gaap_LiabilitiesCurrent_019fd7b0-fb2a-7c45-a8eb-d78c37c9d87c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_LongTermDebtExcludingCurrentMaturitiesAndLongTermConvertibleDebt_019fd7b0-fb2a-780f-98ea-37e7a97ac159" xlink:href="mir-20260930.xsd#mir_LongTermDebtExcludingCurrentMaturitiesAndLongTermConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019fd7b0-fb2a-7967-ac07-2af256352082" xlink:to="loc_mir_LongTermDebtExcludingCurrentMaturitiesAndLongTermConvertibleDebt_019fd7b0-fb2a-780f-98ea-37e7a97ac159" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtNoncurrent_019fd7b0-fb2a-77eb-b752-f2fe16cb9bde" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019fd7b0-fb2a-7967-ac07-2af256352082" xlink:to="loc_us-gaap_ConvertibleDebtNoncurrent_019fd7b0-fb2a-77eb-b752-f2fe16cb9bde" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_019fd7b0-fb2a-7ea2-83e9-a9f65e6ee205" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019fd7b0-fb2a-7967-ac07-2af256352082" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_019fd7b0-fb2a-7ea2-83e9-a9f65e6ee205" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019fd7b0-fb2a-7380-9c75-882343b03614" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019fd7b0-fb2a-7967-ac07-2af256352082" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019fd7b0-fb2a-7380-9c75-882343b03614" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_019fd7b0-fb2a-7092-9566-e4eeb91550a4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019fd7b0-fb2a-7967-ac07-2af256352082" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_019fd7b0-fb2a-7092-9566-e4eeb91550a4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019fd7b0-fb2a-791b-8f1c-a49f742f9ffa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019fd7b0-fb2a-7967-ac07-2af256352082" xlink:to="loc_us-gaap_Liabilities_019fd7b0-fb2a-791b-8f1c-a49f742f9ffa" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_019fd7b0-fb2a-7165-b195-35e0c14e3051" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019fd7b0-fb2a-7967-ac07-2af256352082" xlink:to="loc_us-gaap_CommitmentsAndContingencies_019fd7b0-fb2a-7165-b195-35e0c14e3051" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_019fd7b0-fb2a-782d-8755-c7794efcd798" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019fd7b0-fb2a-7967-ac07-2af256352082" xlink:to="loc_us-gaap_StockholdersEquityAbstract_019fd7b0-fb2a-782d-8755-c7794efcd798" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValueOutstanding_019fd7b0-fb2a-7801-aa8d-59fa8feb168a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValueOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019fd7b0-fb2a-782d-8755-c7794efcd798" xlink:to="loc_us-gaap_CommonStockValueOutstanding_019fd7b0-fb2a-7801-aa8d-59fa8feb168a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonValue_019fd7b0-fb2a-7b26-a96a-09093fe430d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019fd7b0-fb2a-782d-8755-c7794efcd798" xlink:to="loc_us-gaap_TreasuryStockCommonValue_019fd7b0-fb2a-7b26-a96a-09093fe430d0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapital_019fd7b0-fb2a-7e6e-8de7-f7ff5495635c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019fd7b0-fb2a-782d-8755-c7794efcd798" xlink:to="loc_us-gaap_AdditionalPaidInCapital_019fd7b0-fb2a-7e6e-8de7-f7ff5495635c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019fd7b0-fb2a-741f-a884-fde00c2ad994" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019fd7b0-fb2a-782d-8755-c7794efcd798" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019fd7b0-fb2a-741f-a884-fde00c2ad994" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019fd7b0-fb2a-76c9-a112-f81338141bbe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019fd7b0-fb2a-782d-8755-c7794efcd798" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019fd7b0-fb2a-76c9-a112-f81338141bbe" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019fd7b0-fb2a-7791-8501-c16b4c941904" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019fd7b0-fb2a-782d-8755-c7794efcd798" xlink:to="loc_us-gaap_StockholdersEquity_019fd7b0-fb2a-7791-8501-c16b4c941904" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterest_019fd7b0-fb2a-77ab-a20a-1478c4732293" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MinorityInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019fd7b0-fb2a-782d-8755-c7794efcd798" xlink:to="loc_us-gaap_MinorityInterest_019fd7b0-fb2a-77ab-a20a-1478c4732293" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019fd7b0-fb2a-7bca-a0b1-9f52f9aa218d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019fd7b0-fb2a-782d-8755-c7794efcd798" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019fd7b0-fb2a-7bca-a0b1-9f52f9aa218d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_019fd7b0-fb2a-7242-8e1c-5f770c38285c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019fd7b0-fb2a-7967-ac07-2af256352082" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_019fd7b0-fb2a-7242-8e1c-5f770c38285c" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="simple" xlink:href="mir-20260930.xsd#CondensedConsolidatedBalanceSheetsParenthetical"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7121-aaef-723c15b160dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019fd7b0-fb2a-7cbd-94c2-3ee157574719" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7121-aaef-723c15b160dc" xlink:to="loc_us-gaap_StatementTable_019fd7b0-fb2a-7cbd-94c2-3ee157574719" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7d69-8f46-ba78913ade8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019fd7b0-fb2a-7cbd-94c2-3ee157574719" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7d69-8f46-ba78913ade8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7d69-8f46-ba78913ade8e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7d69-8f46-ba78913ade8e" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7d69-8f46-ba78913ade8e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-79db-b8bd-0cdb70598c60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7d69-8f46-ba78913ade8e" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-79db-b8bd-0cdb70598c60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019fd7b0-fb2a-7464-b533-42b7876d60e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-79db-b8bd-0cdb70598c60" xlink:to="loc_us-gaap_CommonClassAMember_019fd7b0-fb2a-7464-b533-42b7876d60e8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019fd7b0-fb2a-761b-a473-34dd6d7ffd4f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-79db-b8bd-0cdb70598c60" xlink:to="loc_us-gaap_CommonClassBMember_019fd7b0-fb2a-761b-a473-34dd6d7ffd4f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019fd7b0-fb2a-7777-a113-2ec3f1bc7322" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7121-aaef-723c15b160dc" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019fd7b0-fb2a-7777-a113-2ec3f1bc7322" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019fd7b0-fb2a-77ac-b07a-58033ed81899" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7121-aaef-723c15b160dc" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019fd7b0-fb2a-77ac-b07a-58033ed81899" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019fd7b0-fb2a-7bde-aebb-ef5f2f3c23bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7121-aaef-723c15b160dc" xlink:to="loc_us-gaap_CommonStockSharesIssued_019fd7b0-fb2a-7bde-aebb-ef5f2f3c23bf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019fd7b0-fb2a-70f1-8188-81a528ceb925" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7121-aaef-723c15b160dc" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019fd7b0-fb2a-70f1-8188-81a528ceb925" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_019fd7b0-fb2a-7d24-ba23-f24be37c51ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7121-aaef-723c15b160dc" xlink:to="loc_us-gaap_TreasuryStockCommonShares_019fd7b0-fb2a-7d24-ba23-f24be37c51ad" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/CondensedConsolidatedStatementsofOperations" xlink:type="simple" xlink:href="mir-20260930.xsd#CondensedConsolidatedStatementsofOperations"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/CondensedConsolidatedStatementsofOperations" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7662-b558-cd55fb1d1cb9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019fd7b0-fb2a-7a9e-92e5-6e3cfd3773a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7662-b558-cd55fb1d1cb9" xlink:to="loc_us-gaap_StatementTable_019fd7b0-fb2a-7a9e-92e5-6e3cfd3773a0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019fd7b0-fb2a-7dc1-b176-b814e2cad976" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019fd7b0-fb2a-7a9e-92e5-6e3cfd3773a0" xlink:to="loc_srt_ProductOrServiceAxis_019fd7b0-fb2a-7dc1-b176-b814e2cad976" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7dc1-b176-b814e2cad976_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019fd7b0-fb2a-7dc1-b176-b814e2cad976" xlink:to="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7dc1-b176-b814e2cad976_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-73c5-a4b5-e06b14e55c12" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019fd7b0-fb2a-7dc1-b176-b814e2cad976" xlink:to="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-73c5-a4b5-e06b14e55c12" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_019fd7b0-fb2a-7e2f-8793-20074eac3be9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-73c5-a4b5-e06b14e55c12" xlink:to="loc_us-gaap_ProductMember_019fd7b0-fb2a-7e2f-8793-20074eac3be9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceMember_019fd7b0-fb2a-7dab-9a36-75a8028d9b0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-73c5-a4b5-e06b14e55c12" xlink:to="loc_us-gaap_ServiceMember_019fd7b0-fb2a-7dab-9a36-75a8028d9b0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fd7b0-fb2a-7a6c-935f-72c341cfbce9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019fd7b0-fb2a-7a9e-92e5-6e3cfd3773a0" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fd7b0-fb2a-7a6c-935f-72c341cfbce9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019fd7b0-fb2a-7a6c-935f-72c341cfbce9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fd7b0-fb2a-7a6c-935f-72c341cfbce9" xlink:to="loc_us-gaap_RelatedPartyDomain_019fd7b0-fb2a-7a6c-935f-72c341cfbce9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019fd7b0-fb2a-7d62-b7c4-6ee2f8dc3e53" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fd7b0-fb2a-7a6c-935f-72c341cfbce9" xlink:to="loc_us-gaap_RelatedPartyDomain_019fd7b0-fb2a-7d62-b7c4-6ee2f8dc3e53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrelatedPartyMember_019fd7b0-fb2a-7422-b891-595df797201f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonrelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019fd7b0-fb2a-7d62-b7c4-6ee2f8dc3e53" xlink:to="loc_us-gaap_NonrelatedPartyMember_019fd7b0-fb2a-7422-b891-595df797201f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_019fd7b0-fb2a-7eeb-ba25-9dd47f1a6df4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7662-b558-cd55fb1d1cb9" xlink:to="loc_us-gaap_RevenuesAbstract_019fd7b0-fb2a-7eeb-ba25-9dd47f1a6df4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019fd7b0-fb2a-7350-8b33-afb9cac9dffc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_019fd7b0-fb2a-7eeb-ba25-9dd47f1a6df4" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019fd7b0-fb2a-7350-8b33-afb9cac9dffc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenueAbstract_019fd7b0-fb2a-7aed-b52b-895c76b7586f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfRevenueAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7662-b558-cd55fb1d1cb9" xlink:to="loc_us-gaap_CostOfRevenueAbstract_019fd7b0-fb2a-7aed-b52b-895c76b7586f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_019fd7b0-fb2a-7682-a96e-97145df23d8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostOfRevenueAbstract_019fd7b0-fb2a-7aed-b52b-895c76b7586f" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_019fd7b0-fb2a-7682-a96e-97145df23d8a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossProfit_019fd7b0-fb2a-7f0c-a784-465a6ad78710" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GrossProfit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7662-b558-cd55fb1d1cb9" xlink:to="loc_us-gaap_GrossProfit_019fd7b0-fb2a-7f0c-a784-465a6ad78710" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_019fd7b0-fb2a-792d-b51b-95e62d78cd71" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7662-b558-cd55fb1d1cb9" xlink:to="loc_us-gaap_OperatingExpensesAbstract_019fd7b0-fb2a-792d-b51b-95e62d78cd71" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019fd7b0-fb2a-7b46-83f6-9f3bbd34d3d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019fd7b0-fb2a-792d-b51b-95e62d78cd71" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019fd7b0-fb2a-7b46-83f6-9f3bbd34d3d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019fd7b0-fb2a-7529-8edc-51c3163f068e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019fd7b0-fb2a-792d-b51b-95e62d78cd71" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019fd7b0-fb2a-7529-8edc-51c3163f068e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenses_019fd7b0-fb2a-71ea-992f-d7b9e32cd8ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019fd7b0-fb2a-792d-b51b-95e62d78cd71" xlink:to="loc_us-gaap_OperatingExpenses_019fd7b0-fb2a-71ea-992f-d7b9e32cd8ad" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019fd7b0-fb2a-7d7a-8262-436be8d19e00" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7662-b558-cd55fb1d1cb9" xlink:to="loc_us-gaap_OperatingIncomeLoss_019fd7b0-fb2a-7d7a-8262-436be8d19e00" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIncomeAndExpensesAbstract_019fd7b0-fb2a-7c8c-9ea5-67544ebe24e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherIncomeAndExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7662-b558-cd55fb1d1cb9" xlink:to="loc_us-gaap_OtherIncomeAndExpensesAbstract_019fd7b0-fb2a-7c8c-9ea5-67544ebe24e5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_019fd7b0-fb2a-7f95-be0f-57716b0f0b06" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIncomeAndExpensesAbstract_019fd7b0-fb2a-7c8c-9ea5-67544ebe24e5" xlink:to="loc_us-gaap_InterestExpenseNonoperating_019fd7b0-fb2a-7f95-be0f-57716b0f0b06" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInterest_019fd7b0-fb2a-7afe-8503-0a76e450cd7d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIncomeAndExpensesAbstract_019fd7b0-fb2a-7c8c-9ea5-67544ebe24e5" xlink:to="loc_us-gaap_InvestmentIncomeInterest_019fd7b0-fb2a-7afe-8503-0a76e450cd7d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019fd7b0-fb2a-777a-8404-801dee8db071" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIncomeAndExpensesAbstract_019fd7b0-fb2a-7c8c-9ea5-67544ebe24e5" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019fd7b0-fb2a-777a-8404-801dee8db071" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyTransactionGainLossBeforeTax_019fd7b0-fb2a-72e0-9b9c-1082e5365905" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignCurrencyTransactionGainLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIncomeAndExpensesAbstract_019fd7b0-fb2a-7c8c-9ea5-67544ebe24e5" xlink:to="loc_us-gaap_ForeignCurrencyTransactionGainLossBeforeTax_019fd7b0-fb2a-72e0-9b9c-1082e5365905" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019fd7b0-fb2a-74de-a773-4e1a030c3106" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIncomeAndExpensesAbstract_019fd7b0-fb2a-7c8c-9ea5-67544ebe24e5" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019fd7b0-fb2a-74de-a773-4e1a030c3106" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019fd7b0-fb2a-7933-aecd-cd368aecf2ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7662-b558-cd55fb1d1cb9" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019fd7b0-fb2a-7933-aecd-cd368aecf2ae" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019fd7b0-fb2a-7096-aa0f-0b17c6b1366e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7662-b558-cd55fb1d1cb9" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019fd7b0-fb2a-7096-aa0f-0b17c6b1366e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019fd7b0-fb2a-76f2-b401-2f384540281f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7662-b558-cd55fb1d1cb9" xlink:to="loc_us-gaap_ProfitLoss_019fd7b0-fb2a-76f2-b401-2f384540281f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_019fd7b0-fb2a-7ab7-9ffa-488ef7f3227c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7662-b558-cd55fb1d1cb9" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_019fd7b0-fb2a-7ab7-9ffa-488ef7f3227c" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019fd7b0-fb2a-7f26-8d73-35caf72689ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7662-b558-cd55fb1d1cb9" xlink:to="loc_us-gaap_NetIncomeLoss_019fd7b0-fb2a-7f26-8d73-35caf72689ec" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareAbstract_019fd7b0-fb2a-77ca-83f2-0bb08cfdb643" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7662-b558-cd55fb1d1cb9" xlink:to="loc_us-gaap_EarningsPerShareAbstract_019fd7b0-fb2a-77ca-83f2-0bb08cfdb643" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_019fd7b0-fb2a-78bf-95b4-7f295302fe67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_019fd7b0-fb2a-77ca-83f2-0bb08cfdb643" xlink:to="loc_us-gaap_EarningsPerShareBasic_019fd7b0-fb2a-78bf-95b4-7f295302fe67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_019fd7b0-fb2a-78c6-94cb-4170735c02df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_019fd7b0-fb2a-77ca-83f2-0bb08cfdb643" xlink:to="loc_us-gaap_EarningsPerShareDiluted_019fd7b0-fb2a-78c6-94cb-4170735c02df" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019fd7b0-fb2a-7dc0-8e0b-f382a6b2c8ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-7662-b558-cd55fb1d1cb9" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019fd7b0-fb2a-7dc0-8e0b-f382a6b2c8ae" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019fd7b0-fb2a-7fcb-92f9-5c0e2883f9ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019fd7b0-fb2a-7dc0-8e0b-f382a6b2c8ae" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019fd7b0-fb2a-7fcb-92f9-5c0e2883f9ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019fd7b0-fb2a-79f1-abec-9670eaf09d8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019fd7b0-fb2a-7dc0-8e0b-f382a6b2c8ae" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019fd7b0-fb2a-79f1-abec-9670eaf09d8e" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/CondensedConsolidatedStatementsofStockholdersEquity" xlink:type="simple" xlink:href="mir-20260930.xsd#CondensedConsolidatedStatementsofStockholdersEquity"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/CondensedConsolidatedStatementsofStockholdersEquity" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-726d-83cb-bf7ddb8231a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019fd7b0-fb2a-7882-816a-5dbf2d9bd8e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-726d-83cb-bf7ddb8231a1" xlink:to="loc_us-gaap_StatementTable_019fd7b0-fb2a-7882-816a-5dbf2d9bd8e0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019fd7b0-fb2a-7852-a3ee-6eafa5b9ac6b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019fd7b0-fb2a-7882-816a-5dbf2d9bd8e0" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019fd7b0-fb2a-7852-a3ee-6eafa5b9ac6b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fd7b0-fb2a-7852-a3ee-6eafa5b9ac6b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019fd7b0-fb2a-7852-a3ee-6eafa5b9ac6b" xlink:to="loc_us-gaap_EquityComponentDomain_019fd7b0-fb2a-7852-a3ee-6eafa5b9ac6b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fd7b0-fb2a-7fac-b37d-a09e27496084" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019fd7b0-fb2a-7852-a3ee-6eafa5b9ac6b" xlink:to="loc_us-gaap_EquityComponentDomain_019fd7b0-fb2a-7fac-b37d-a09e27496084" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019fd7b0-fb2a-7f4c-aae2-45ed43cc7a2c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd7b0-fb2a-7fac-b37d-a09e27496084" xlink:to="loc_us-gaap_CommonStockMember_019fd7b0-fb2a-7f4c-aae2-45ed43cc7a2c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_019fd7b0-fb2a-710d-b767-6c5cdfee035e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd7b0-fb2a-7fac-b37d-a09e27496084" xlink:to="loc_us-gaap_TreasuryStockCommonMember_019fd7b0-fb2a-710d-b767-6c5cdfee035e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019fd7b0-fb2a-7d07-8381-c663d3b48a14" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd7b0-fb2a-7fac-b37d-a09e27496084" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019fd7b0-fb2a-7d07-8381-c663d3b48a14" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019fd7b0-fb2a-717b-b62f-905b1a96badc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd7b0-fb2a-7fac-b37d-a09e27496084" xlink:to="loc_us-gaap_RetainedEarningsMember_019fd7b0-fb2a-717b-b62f-905b1a96badc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fd7b0-fb2a-781c-95fb-1a451b74f910" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd7b0-fb2a-7fac-b37d-a09e27496084" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fd7b0-fb2a-781c-95fb-1a451b74f910" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_019fd7b0-fb2a-7e3d-9c80-ee3d62873cb6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd7b0-fb2a-7fac-b37d-a09e27496084" xlink:to="loc_us-gaap_NoncontrollingInterestMember_019fd7b0-fb2a-7e3d-9c80-ee3d62873cb6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7168-9bf0-8e0892eb9254" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019fd7b0-fb2a-7882-816a-5dbf2d9bd8e0" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7168-9bf0-8e0892eb9254" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7168-9bf0-8e0892eb9254_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7168-9bf0-8e0892eb9254" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7168-9bf0-8e0892eb9254_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-721b-a7b5-22012d6c2526" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7168-9bf0-8e0892eb9254" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-721b-a7b5-22012d6c2526" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019fd7b0-fb2a-7210-ab9e-82055ffc0f4f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-721b-a7b5-22012d6c2526" xlink:to="loc_us-gaap_CommonClassAMember_019fd7b0-fb2a-7210-ab9e-82055ffc0f4f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019fd7b0-fb2a-7cca-80be-e603db7bf3fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-721b-a7b5-22012d6c2526" xlink:to="loc_us-gaap_CommonClassBMember_019fd7b0-fb2a-7cca-80be-e603db7bf3fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019fd7b0-fb2a-77e8-bb5d-e9ba4d48bd0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockByUniqueDescriptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019fd7b0-fb2a-7882-816a-5dbf2d9bd8e0" xlink:to="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019fd7b0-fb2a-77e8-bb5d-e9ba4d48bd0c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_019fd7b0-fb2a-77e8-bb5d-e9ba4d48bd0c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019fd7b0-fb2a-77e8-bb5d-e9ba4d48bd0c" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_019fd7b0-fb2a-77e8-bb5d-e9ba4d48bd0c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_019fd7b0-fb2a-710f-b24b-355c0894a219" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019fd7b0-fb2a-77e8-bb5d-e9ba4d48bd0c" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_019fd7b0-fb2a-710f-b24b-355c0894a219" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ConversionOfClassBCommonStockToClassACommonStockMember_019fd7b0-fb2a-7e5e-9b78-32c1bdc2b372" xlink:href="mir-20260930.xsd#mir_ConversionOfClassBCommonStockToClassACommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_019fd7b0-fb2a-710f-b24b-355c0894a219" xlink:to="loc_mir_ConversionOfClassBCommonStockToClassACommonStockMember_019fd7b0-fb2a-7e5e-9b78-32c1bdc2b372" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd7b0-fb2a-726d-83cb-bf7ddb8231a1" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019fd7b0-fb2a-7a79-b798-314ea54f3afc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019fd7b0-fb2a-7a79-b798-314ea54f3afc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019fd7b0-fb2a-7c43-a12c-08c92ce6abe3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019fd7b0-fb2a-7c43-a12c-08c92ce6abe3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_019fd7b0-fb2a-7c3a-9ed5-261e29aa05bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_us-gaap_TreasuryStockCommonShares_019fd7b0-fb2a-7c3a-9ed5-261e29aa05bd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_019fd7b0-fb2a-7255-951d-dfc96bb3566d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_019fd7b0-fb2a-7255-951d-dfc96bb3566d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued_019fd7b0-fb2a-7ec9-bb4a-ef3547e55230" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued_019fd7b0-fb2a-7ec9-bb4a-ef3547e55230" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueTreasuryStockReissued_019fd7b0-fb2a-7194-8084-394fbeb8223a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueTreasuryStockReissued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueTreasuryStockReissued_019fd7b0-fb2a-7194-8084-394fbeb8223a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_019fd7b0-fb2a-7172-a1bc-3225ee9ded06" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_019fd7b0-fb2a-7172-a1bc-3225ee9ded06" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_019fd7b0-fb2a-7e6d-84ef-dbf7e1b34f10" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_019fd7b0-fb2a-7e6d-84ef-dbf7e1b34f10" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_019fd7b0-fb2a-755f-812b-23172894c7d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesIssuedForServices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_019fd7b0-fb2a-755f-812b-23172894c7d0" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueIssuedForServices_019fd7b0-fb2a-70b5-be2f-b02491a5c658" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueIssuedForServices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueIssuedForServices_019fd7b0-fb2a-70b5-be2f-b02491a5c658" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_019fd7b0-fb2a-759b-9a34-ce87d7779056" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_019fd7b0-fb2a-759b-9a34-ce87d7779056" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_019fd7b0-fb2a-7d7f-89c2-89e4f24e81a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_019fd7b0-fb2a-7d7f-89c2-89e4f24e81a2" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_01a031d3-f2fa-73c1-9de6-fc188b2f75f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_01a031d3-f2fa-73c1-9de6-fc188b2f75f8" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_01a031d8-d103-7cd4-bb59-e8911a520e22" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_01a031d8-d103-7cd4-bb59-e8911a520e22" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_019fd7b0-fb2a-7487-a642-ae60502df796" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_019fd7b0-fb2a-7487-a642-ae60502df796" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_019fd7b0-fb2a-70e2-8abb-ad92280fe157" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_019fd7b0-fb2a-70e2-8abb-ad92280fe157" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_TreasuryStockValueAcquiredExciseTax_01a12083-4788-782d-b786-9eace2bf1d1d" xlink:href="mir-20260930.xsd#mir_TreasuryStockValueAcquiredExciseTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_mir_TreasuryStockValueAcquiredExciseTax_01a12083-4788-782d-b786-9eace2bf1d1d" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_AdjustmentsToAdditionalPaidInCapitalPurchasesOfCappedCalls_019fd7b0-fb2a-7daf-be18-4802bf57d9d5" xlink:href="mir-20260930.xsd#mir_AdjustmentsToAdditionalPaidInCapitalPurchasesOfCappedCalls"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_mir_AdjustmentsToAdditionalPaidInCapitalPurchasesOfCappedCalls_019fd7b0-fb2a-7daf-be18-4802bf57d9d5" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_AdjustmentsToAdditionalPaidInCapitalTaxImpactOfCappedCallsRelatedToConvertibleDebt_019fd7b0-fb2a-71db-bd37-124e058f1800" xlink:href="mir-20260930.xsd#mir_AdjustmentsToAdditionalPaidInCapitalTaxImpactOfCappedCallsRelatedToConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_mir_AdjustmentsToAdditionalPaidInCapitalTaxImpactOfCappedCallsRelatedToConvertibleDebt_019fd7b0-fb2a-71db-bd37-124e058f1800" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019fd7b0-fb2a-70ee-aa16-583c4f70678c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019fd7b0-fb2a-70ee-aa16-583c4f70678c" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019fd7b0-fb2a-71ec-9c60-c2b4c3ff7902" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_us-gaap_ProfitLoss_019fd7b0-fb2a-71ec-9c60-c2b4c3ff7902" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019fd7b0-fb2a-772f-b487-9a780958722d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd7b0-fb2a-7f46-9218-385ebfca5ceb" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019fd7b0-fb2a-772f-b487-9a780958722d" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019fd7b0-fb2a-72b8-b793-1d031c626c60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019fd7b0-fb2a-73b2-95a9-43de838cd06f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_019fd7b0-fb2a-7897-8f74-16a017374378" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonShares"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/NatureofBusinessandSummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#NatureofBusinessandSummaryofSignificantAccountingPoliciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/NatureofBusinessandSummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:href="mir-20260930.xsd#mir_SummaryOfSignificantAccountingPolicyLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:href="mir-20260930.xsd#mir_SummaryOfSignificantAccountingPolicyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfFinancialPositionLocationBalanceAxis_019fd7b0-fb2a-7cb0-8953-b8c27ab1a931" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfFinancialPositionLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_StatementOfFinancialPositionLocationBalanceAxis_019fd7b0-fb2a-7cb0-8953-b8c27ab1a931" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fb2a-7f87-ad7e-ef85887ca329" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fb2a-7f87-ad7e-ef85887ca329" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7f87-ad7e-ef85887ca329_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fb2a-7f87-ad7e-ef85887ca329" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7f87-ad7e-ef85887ca329_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7a08-90de-1fde25bd3cde" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fb2a-7f87-ad7e-ef85887ca329" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7a08-90de-1fde25bd3cde" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ConvertibleSeniorNotesDue2030NotesMember_019fd7b0-fb2a-7aa2-b9c5-f71a24c23d08" xlink:href="mir-20260930.xsd#mir_ConvertibleSeniorNotesDue2030NotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7a08-90de-1fde25bd3cde" xlink:to="loc_mir_ConvertibleSeniorNotesDue2030NotesMember_019fd7b0-fb2a-7aa2-b9c5-f71a24c23d08" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ConvertibleSeniorNotesDue2031NotesMember_019fd7b0-fb2a-72b3-9405-644c42b9971a" xlink:href="mir-20260930.xsd#mir_ConvertibleSeniorNotesDue2031NotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7a08-90de-1fde25bd3cde" xlink:to="loc_mir_ConvertibleSeniorNotesDue2031NotesMember_019fd7b0-fb2a-72b3-9405-644c42b9971a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fb2a-7c34-bbfc-27776f6296e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fb2a-7c34-bbfc-27776f6296e5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fb2a-7c34-bbfc-27776f6296e5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fb2a-7c34-bbfc-27776f6296e5" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fb2a-7c34-bbfc-27776f6296e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fb2a-7401-826b-2adf7db5a16e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fb2a-7c34-bbfc-27776f6296e5" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fb2a-7401-826b-2adf7db5a16e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_019fd7b0-fb2a-717b-a7f2-2e5bc1a73836" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fb2a-7401-826b-2adf7db5a16e" xlink:to="loc_us-gaap_ConvertibleDebtMember_019fd7b0-fb2a-717b-a7f2-2e5bc1a73836" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_019fd7b0-fb2a-7951-885c-23e7cd382405" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_019fd7b0-fb2a-7951-885c-23e7cd382405" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7a48-ab15-a2760f408af1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7a48-ab15-a2760f408af1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019fd7b0-fb2a-7397-80b3-6e809d816b9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7a48-ab15-a2760f408af1" xlink:to="loc_us-gaap_CommonClassAMember_019fd7b0-fb2a-7397-80b3-6e809d816b9d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019fd7b0-fb2a-7834-8410-420608ab7519" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_srt_ProductOrServiceAxis_019fd7b0-fb2a-7834-8410-420608ab7519" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7834-8410-420608ab7519_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019fd7b0-fb2a-7834-8410-420608ab7519" xlink:to="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7834-8410-420608ab7519_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7d81-b06e-1de33df8abaa" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019fd7b0-fb2a-7834-8410-420608ab7519" xlink:to="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7d81-b06e-1de33df8abaa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ProjectOneMember_019fd7b0-fb2a-713a-b9bd-b819e4348bae" xlink:href="mir-20260930.xsd#mir_ProjectOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7d81-b06e-1de33df8abaa" xlink:to="loc_mir_ProjectOneMember_019fd7b0-fb2a-713a-b9bd-b819e4348bae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019fd7b0-fb2a-7a8d-b657-33c6fe110792" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019fd7b0-fb2a-7a8d-b657-33c6fe110792" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductConcentrationRiskMember_019fd7b0-fb2a-7950-b7a1-6086a36e051c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019fd7b0-fb2a-7a8d-b657-33c6fe110792" xlink:to="loc_us-gaap_ProductConcentrationRiskMember_019fd7b0-fb2a-7950-b7a1-6086a36e051c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fd7b0-fb2a-7697-8a59-95be300b4cbe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fd7b0-fb2a-7697-8a59-95be300b4cbe" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd7b0-fb2a-7697-8a59-95be300b4cbe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fd7b0-fb2a-7697-8a59-95be300b4cbe" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd7b0-fb2a-7697-8a59-95be300b4cbe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd7b0-fb2a-727d-97be-09de4f725cda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fd7b0-fb2a-7697-8a59-95be300b4cbe" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd7b0-fb2a-727d-97be-09de4f725cda" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ContractAssetBalanceMember_019fd7b0-fb2a-7ddd-b232-11d401898d7d" xlink:href="mir-20260930.xsd#mir_ContractAssetBalanceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd7b0-fb2a-727d-97be-09de4f725cda" xlink:to="loc_mir_ContractAssetBalanceMember_019fd7b0-fb2a-7ddd-b232-11d401898d7d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_019fd7b0-fb2a-7e89-a62b-93cd84e5f9f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_NumberOfOperatingSegments_019fd7b0-fb2a-7e89-a62b-93cd84e5f9f8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_019fd7b0-fb2a-7bd8-b54d-8da2cf177def" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_NumberOfReportableSegments_019fd7b0-fb2a-7bd8-b54d-8da2cf177def" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019fd7b0-fb2a-7f39-ae5a-c7009e557578" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019fd7b0-fb2a-7f39-ae5a-c7009e557578" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetRetirementObligation_019fd7b0-fb2a-713f-b1cf-524348f8f767" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetRetirementObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_AssetRetirementObligation_019fd7b0-fb2a-713f-b1cf-524348f8f767" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019fd7b0-fb2a-7b9e-9428-82d80bb2e731" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019fd7b0-fb2a-7b9e-9428-82d80bb2e731" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019fd7b0-fb2a-7517-8c23-7d096bacb881" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019fd7b0-fb2a-7517-8c23-7d096bacb881" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019fd7b0-fb2a-756f-b595-7a17403c2f0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019fd7b0-fb2a-756f-b595-7a17403c2f0b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_RemainingPerformanceObligationsCustomerContract_019fd7b0-fb2a-7c76-b4b4-2cb2063d5f36" xlink:href="mir-20260930.xsd#mir_RemainingPerformanceObligationsCustomerContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_mir_RemainingPerformanceObligationsCustomerContract_019fd7b0-fb2a-7c76-b4b4-2cb2063d5f36" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_019fd7b0-fb2a-78fb-96d1-40bd2a1dc013" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_019fd7b0-fb2a-78fb-96d1-40bd2a1dc013" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019fd7b0-fb2a-7d36-aa5d-6da707f6c222" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019fd7b0-fb2a-7d36-aa5d-6da707f6c222" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/NatureofBusinessandSummaryofSignificantAccountingPoliciesNarrativeDetails_1" xlink:type="simple" xlink:href="mir-20260930.xsd#NatureofBusinessandSummaryofSignificantAccountingPoliciesNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/NatureofBusinessandSummaryofSignificantAccountingPoliciesNarrativeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:href="mir-20260930.xsd#mir_SummaryOfSignificantAccountingPolicyLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:href="mir-20260930.xsd#mir_SummaryOfSignificantAccountingPolicyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fb2a-7f87-ad7e-ef85887ca329" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fb2a-7f87-ad7e-ef85887ca329" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7f87-ad7e-ef85887ca329_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fb2a-7f87-ad7e-ef85887ca329" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7f87-ad7e-ef85887ca329_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7a08-90de-1fde25bd3cde" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fb2a-7f87-ad7e-ef85887ca329" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7a08-90de-1fde25bd3cde" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ConvertibleSeniorNotesDue2030NotesMember_019fd7b0-fb2a-7aa2-b9c5-f71a24c23d08" xlink:href="mir-20260930.xsd#mir_ConvertibleSeniorNotesDue2030NotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7a08-90de-1fde25bd3cde" xlink:to="loc_mir_ConvertibleSeniorNotesDue2030NotesMember_019fd7b0-fb2a-7aa2-b9c5-f71a24c23d08" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ConvertibleSeniorNotesDue2031NotesMember_019fd7b0-fb2a-72b3-9405-644c42b9971a" xlink:href="mir-20260930.xsd#mir_ConvertibleSeniorNotesDue2031NotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7a08-90de-1fde25bd3cde" xlink:to="loc_mir_ConvertibleSeniorNotesDue2031NotesMember_019fd7b0-fb2a-72b3-9405-644c42b9971a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fb2a-7c34-bbfc-27776f6296e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fb2a-7c34-bbfc-27776f6296e5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fb2a-7c34-bbfc-27776f6296e5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fb2a-7c34-bbfc-27776f6296e5" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fb2a-7c34-bbfc-27776f6296e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fb2a-7401-826b-2adf7db5a16e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fb2a-7c34-bbfc-27776f6296e5" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fb2a-7401-826b-2adf7db5a16e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_019fd7b0-fb2a-717b-a7f2-2e5bc1a73836" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fb2a-7401-826b-2adf7db5a16e" xlink:to="loc_us-gaap_ConvertibleDebtMember_019fd7b0-fb2a-717b-a7f2-2e5bc1a73836" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7a48-ab15-a2760f408af1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7a48-ab15-a2760f408af1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019fd7b0-fb2a-7397-80b3-6e809d816b9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7a48-ab15-a2760f408af1" xlink:to="loc_us-gaap_CommonClassAMember_019fd7b0-fb2a-7397-80b3-6e809d816b9d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019fd7b0-fb2a-7834-8410-420608ab7519" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_srt_ProductOrServiceAxis_019fd7b0-fb2a-7834-8410-420608ab7519" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7834-8410-420608ab7519_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019fd7b0-fb2a-7834-8410-420608ab7519" xlink:to="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7834-8410-420608ab7519_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7d81-b06e-1de33df8abaa" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019fd7b0-fb2a-7834-8410-420608ab7519" xlink:to="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7d81-b06e-1de33df8abaa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ProjectOneMember_019fd7b0-fb2a-713a-b9bd-b819e4348bae" xlink:href="mir-20260930.xsd#mir_ProjectOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7d81-b06e-1de33df8abaa" xlink:to="loc_mir_ProjectOneMember_019fd7b0-fb2a-713a-b9bd-b819e4348bae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019fd7b0-fb2a-7a8d-b657-33c6fe110792" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019fd7b0-fb2a-7a8d-b657-33c6fe110792" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductConcentrationRiskMember_019fd7b0-fb2a-7950-b7a1-6086a36e051c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019fd7b0-fb2a-7a8d-b657-33c6fe110792" xlink:to="loc_us-gaap_ProductConcentrationRiskMember_019fd7b0-fb2a-7950-b7a1-6086a36e051c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fd7b0-fb2a-7697-8a59-95be300b4cbe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fd7b0-fb2a-7697-8a59-95be300b4cbe" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd7b0-fb2a-7697-8a59-95be300b4cbe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fd7b0-fb2a-7697-8a59-95be300b4cbe" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd7b0-fb2a-7697-8a59-95be300b4cbe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd7b0-fb2a-727d-97be-09de4f725cda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fd7b0-fb2a-7697-8a59-95be300b4cbe" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd7b0-fb2a-727d-97be-09de4f725cda" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ContractAssetBalanceMember_019fd7b0-fb2a-7ddd-b232-11d401898d7d" xlink:href="mir-20260930.xsd#mir_ContractAssetBalanceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd7b0-fb2a-727d-97be-09de4f725cda" xlink:to="loc_mir_ContractAssetBalanceMember_019fd7b0-fb2a-7ddd-b232-11d401898d7d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_019fd7b0-fb2a-7e89-a62b-93cd84e5f9f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_NumberOfOperatingSegments_019fd7b0-fb2a-7e89-a62b-93cd84e5f9f8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_019fd7b0-fb2a-7bd8-b54d-8da2cf177def" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_NumberOfReportableSegments_019fd7b0-fb2a-7bd8-b54d-8da2cf177def" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019fd7b0-fb2a-7f39-ae5a-c7009e557578" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019fd7b0-fb2a-7f39-ae5a-c7009e557578" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetRetirementObligation_019fd7b0-fb2a-713f-b1cf-524348f8f767" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetRetirementObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_AssetRetirementObligation_019fd7b0-fb2a-713f-b1cf-524348f8f767" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019fd7b0-fb2a-7b9e-9428-82d80bb2e731" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019fd7b0-fb2a-7b9e-9428-82d80bb2e731" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019fd7b0-fb2a-7517-8c23-7d096bacb881" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019fd7b0-fb2a-7517-8c23-7d096bacb881" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019fd7b0-fb2a-756f-b595-7a17403c2f0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019fd7b0-fb2a-756f-b595-7a17403c2f0b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_RemainingPerformanceObligationsCustomerContract_019fd7b0-fb2a-7c76-b4b4-2cb2063d5f36" xlink:href="mir-20260930.xsd#mir_RemainingPerformanceObligationsCustomerContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_mir_RemainingPerformanceObligationsCustomerContract_019fd7b0-fb2a-7c76-b4b4-2cb2063d5f36" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_019fd7b0-fb2a-78fb-96d1-40bd2a1dc013" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_019fd7b0-fb2a-78fb-96d1-40bd2a1dc013" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019fd7b0-fb2a-7d36-aa5d-6da707f6c222" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019fd7b0-fb2a-7d36-aa5d-6da707f6c222" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/NatureofBusinessandSummaryofSignificantAccountingPoliciesNarrativeDetails_2" xlink:type="simple" xlink:href="mir-20260930.xsd#NatureofBusinessandSummaryofSignificantAccountingPoliciesNarrativeDetails_2"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/NatureofBusinessandSummaryofSignificantAccountingPoliciesNarrativeDetails_2" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:href="mir-20260930.xsd#mir_SummaryOfSignificantAccountingPolicyLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:href="mir-20260930.xsd#mir_SummaryOfSignificantAccountingPolicyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fb2a-7f87-ad7e-ef85887ca329" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fb2a-7f87-ad7e-ef85887ca329" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7f87-ad7e-ef85887ca329_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fb2a-7f87-ad7e-ef85887ca329" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7f87-ad7e-ef85887ca329_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7a08-90de-1fde25bd3cde" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fb2a-7f87-ad7e-ef85887ca329" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7a08-90de-1fde25bd3cde" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ConvertibleSeniorNotesDue2030NotesMember_019fd7b0-fb2a-7aa2-b9c5-f71a24c23d08" xlink:href="mir-20260930.xsd#mir_ConvertibleSeniorNotesDue2030NotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7a08-90de-1fde25bd3cde" xlink:to="loc_mir_ConvertibleSeniorNotesDue2030NotesMember_019fd7b0-fb2a-7aa2-b9c5-f71a24c23d08" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ConvertibleSeniorNotesDue2031NotesMember_019fd7b0-fb2a-72b3-9405-644c42b9971a" xlink:href="mir-20260930.xsd#mir_ConvertibleSeniorNotesDue2031NotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7a08-90de-1fde25bd3cde" xlink:to="loc_mir_ConvertibleSeniorNotesDue2031NotesMember_019fd7b0-fb2a-72b3-9405-644c42b9971a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fb2a-7c34-bbfc-27776f6296e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fb2a-7c34-bbfc-27776f6296e5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fb2a-7c34-bbfc-27776f6296e5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fb2a-7c34-bbfc-27776f6296e5" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fb2a-7c34-bbfc-27776f6296e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fb2a-7401-826b-2adf7db5a16e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fb2a-7c34-bbfc-27776f6296e5" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fb2a-7401-826b-2adf7db5a16e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_019fd7b0-fb2a-717b-a7f2-2e5bc1a73836" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fb2a-7401-826b-2adf7db5a16e" xlink:to="loc_us-gaap_ConvertibleDebtMember_019fd7b0-fb2a-717b-a7f2-2e5bc1a73836" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7a48-ab15-a2760f408af1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7a48-ab15-a2760f408af1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019fd7b0-fb2a-7397-80b3-6e809d816b9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7a48-ab15-a2760f408af1" xlink:to="loc_us-gaap_CommonClassAMember_019fd7b0-fb2a-7397-80b3-6e809d816b9d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019fd7b0-fb2a-7834-8410-420608ab7519" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_srt_ProductOrServiceAxis_019fd7b0-fb2a-7834-8410-420608ab7519" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7834-8410-420608ab7519_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019fd7b0-fb2a-7834-8410-420608ab7519" xlink:to="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7834-8410-420608ab7519_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7d81-b06e-1de33df8abaa" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019fd7b0-fb2a-7834-8410-420608ab7519" xlink:to="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7d81-b06e-1de33df8abaa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ProjectOneMember_019fd7b0-fb2a-713a-b9bd-b819e4348bae" xlink:href="mir-20260930.xsd#mir_ProjectOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7d81-b06e-1de33df8abaa" xlink:to="loc_mir_ProjectOneMember_019fd7b0-fb2a-713a-b9bd-b819e4348bae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019fd7b0-fb2a-7a8d-b657-33c6fe110792" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019fd7b0-fb2a-7a8d-b657-33c6fe110792" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductConcentrationRiskMember_019fd7b0-fb2a-7950-b7a1-6086a36e051c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019fd7b0-fb2a-7a8d-b657-33c6fe110792" xlink:to="loc_us-gaap_ProductConcentrationRiskMember_019fd7b0-fb2a-7950-b7a1-6086a36e051c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fd7b0-fb2a-7697-8a59-95be300b4cbe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fd7b0-fb2a-7697-8a59-95be300b4cbe" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd7b0-fb2a-7697-8a59-95be300b4cbe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fd7b0-fb2a-7697-8a59-95be300b4cbe" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd7b0-fb2a-7697-8a59-95be300b4cbe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd7b0-fb2a-727d-97be-09de4f725cda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fd7b0-fb2a-7697-8a59-95be300b4cbe" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd7b0-fb2a-727d-97be-09de4f725cda" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ContractAssetBalanceMember_019fd7b0-fb2a-7ddd-b232-11d401898d7d" xlink:href="mir-20260930.xsd#mir_ContractAssetBalanceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd7b0-fb2a-727d-97be-09de4f725cda" xlink:to="loc_mir_ContractAssetBalanceMember_019fd7b0-fb2a-7ddd-b232-11d401898d7d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfFinancialPositionLocationBalanceAxis_019fd7b0-fb2a-7cb0-8953-b8c27ab1a931" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfFinancialPositionLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_StatementOfFinancialPositionLocationBalanceAxis_019fd7b0-fb2a-7cb0-8953-b8c27ab1a931" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_019fd7b0-fb2a-7e89-a62b-93cd84e5f9f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_NumberOfOperatingSegments_019fd7b0-fb2a-7e89-a62b-93cd84e5f9f8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_019fd7b0-fb2a-7bd8-b54d-8da2cf177def" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_NumberOfReportableSegments_019fd7b0-fb2a-7bd8-b54d-8da2cf177def" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019fd7b0-fb2a-7f39-ae5a-c7009e557578" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019fd7b0-fb2a-7f39-ae5a-c7009e557578" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetRetirementObligation_019fd7b0-fb2a-713f-b1cf-524348f8f767" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetRetirementObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_AssetRetirementObligation_019fd7b0-fb2a-713f-b1cf-524348f8f767" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019fd7b0-fb2a-7b9e-9428-82d80bb2e731" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019fd7b0-fb2a-7b9e-9428-82d80bb2e731" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019fd7b0-fb2a-7517-8c23-7d096bacb881" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019fd7b0-fb2a-7517-8c23-7d096bacb881" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019fd7b0-fb2a-756f-b595-7a17403c2f0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019fd7b0-fb2a-756f-b595-7a17403c2f0b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_RemainingPerformanceObligationsCustomerContract_019fd7b0-fb2a-7c76-b4b4-2cb2063d5f36" xlink:href="mir-20260930.xsd#mir_RemainingPerformanceObligationsCustomerContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_mir_RemainingPerformanceObligationsCustomerContract_019fd7b0-fb2a-7c76-b4b4-2cb2063d5f36" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_019fd7b0-fb2a-78fb-96d1-40bd2a1dc013" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_019fd7b0-fb2a-78fb-96d1-40bd2a1dc013" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019fd7b0-fb2a-7d36-aa5d-6da707f6c222" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019fd7b0-fb2a-7d36-aa5d-6da707f6c222" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/NatureofBusinessandSummaryofSignificantAccountingPoliciesNarrativeDetails_3" xlink:type="simple" xlink:href="mir-20260930.xsd#NatureofBusinessandSummaryofSignificantAccountingPoliciesNarrativeDetails_3"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/NatureofBusinessandSummaryofSignificantAccountingPoliciesNarrativeDetails_3" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:href="mir-20260930.xsd#mir_SummaryOfSignificantAccountingPolicyLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:href="mir-20260930.xsd#mir_SummaryOfSignificantAccountingPolicyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fb2a-7f87-ad7e-ef85887ca329" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fb2a-7f87-ad7e-ef85887ca329" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7f87-ad7e-ef85887ca329_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fb2a-7f87-ad7e-ef85887ca329" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7f87-ad7e-ef85887ca329_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7a08-90de-1fde25bd3cde" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fb2a-7f87-ad7e-ef85887ca329" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7a08-90de-1fde25bd3cde" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ConvertibleSeniorNotesDue2030NotesMember_019fd7b0-fb2a-7aa2-b9c5-f71a24c23d08" xlink:href="mir-20260930.xsd#mir_ConvertibleSeniorNotesDue2030NotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7a08-90de-1fde25bd3cde" xlink:to="loc_mir_ConvertibleSeniorNotesDue2030NotesMember_019fd7b0-fb2a-7aa2-b9c5-f71a24c23d08" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ConvertibleSeniorNotesDue2031NotesMember_019fd7b0-fb2a-72b3-9405-644c42b9971a" xlink:href="mir-20260930.xsd#mir_ConvertibleSeniorNotesDue2031NotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fb2a-7a08-90de-1fde25bd3cde" xlink:to="loc_mir_ConvertibleSeniorNotesDue2031NotesMember_019fd7b0-fb2a-72b3-9405-644c42b9971a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fb2a-7c34-bbfc-27776f6296e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fb2a-7c34-bbfc-27776f6296e5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fb2a-7c34-bbfc-27776f6296e5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fb2a-7c34-bbfc-27776f6296e5" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fb2a-7c34-bbfc-27776f6296e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fb2a-7401-826b-2adf7db5a16e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fb2a-7c34-bbfc-27776f6296e5" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fb2a-7401-826b-2adf7db5a16e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_019fd7b0-fb2a-717b-a7f2-2e5bc1a73836" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fb2a-7401-826b-2adf7db5a16e" xlink:to="loc_us-gaap_ConvertibleDebtMember_019fd7b0-fb2a-717b-a7f2-2e5bc1a73836" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7a48-ab15-a2760f408af1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fb2a-7553-b9cd-7eb1a74d960f" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7a48-ab15-a2760f408af1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019fd7b0-fb2a-7397-80b3-6e809d816b9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd7b0-fb2a-7a48-ab15-a2760f408af1" xlink:to="loc_us-gaap_CommonClassAMember_019fd7b0-fb2a-7397-80b3-6e809d816b9d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019fd7b0-fb2a-7834-8410-420608ab7519" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_srt_ProductOrServiceAxis_019fd7b0-fb2a-7834-8410-420608ab7519" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7834-8410-420608ab7519_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019fd7b0-fb2a-7834-8410-420608ab7519" xlink:to="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7834-8410-420608ab7519_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7d81-b06e-1de33df8abaa" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019fd7b0-fb2a-7834-8410-420608ab7519" xlink:to="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7d81-b06e-1de33df8abaa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ProjectOneMember_019fd7b0-fb2a-713a-b9bd-b819e4348bae" xlink:href="mir-20260930.xsd#mir_ProjectOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019fd7b0-fb2a-7d81-b06e-1de33df8abaa" xlink:to="loc_mir_ProjectOneMember_019fd7b0-fb2a-713a-b9bd-b819e4348bae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019fd7b0-fb2a-7a8d-b657-33c6fe110792" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019fd7b0-fb2a-7c0b-a01f-6989cfb79bf1" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019fd7b0-fb2a-7a8d-b657-33c6fe110792" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductConcentrationRiskMember_019fd7b0-fb2a-7950-b7a1-6086a36e051c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019fd7b0-fb2a-7a8d-b657-33c6fe110792" xlink:to="loc_us-gaap_ProductConcentrationRiskMember_019fd7b0-fb2a-7950-b7a1-6086a36e051c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fd7b0-fb2a-7697-8a59-95be300b4cbe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fd7b0-fb2a-7697-8a59-95be300b4cbe" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd7b0-fb2a-7697-8a59-95be300b4cbe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fd7b0-fb2a-7697-8a59-95be300b4cbe" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd7b0-fb2a-7697-8a59-95be300b4cbe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd7b0-fb2a-727d-97be-09de4f725cda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fd7b0-fb2a-7697-8a59-95be300b4cbe" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd7b0-fb2a-727d-97be-09de4f725cda" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ContractAssetBalanceMember_019fd7b0-fb2a-7ddd-b232-11d401898d7d" xlink:href="mir-20260930.xsd#mir_ContractAssetBalanceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fd7b0-fb2a-727d-97be-09de4f725cda" xlink:to="loc_mir_ContractAssetBalanceMember_019fd7b0-fb2a-7ddd-b232-11d401898d7d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_019fd7b0-fb2a-7951-885c-23e7cd382405" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyTable_019fd7b0-fb2a-7d5f-b3ae-d7e18843b4c8" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_019fd7b0-fb2a-7951-885c-23e7cd382405" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_019fd7b0-fb2a-7e89-a62b-93cd84e5f9f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_NumberOfOperatingSegments_019fd7b0-fb2a-7e89-a62b-93cd84e5f9f8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_019fd7b0-fb2a-7bd8-b54d-8da2cf177def" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_NumberOfReportableSegments_019fd7b0-fb2a-7bd8-b54d-8da2cf177def" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019fd7b0-fb2a-7f39-ae5a-c7009e557578" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019fd7b0-fb2a-7f39-ae5a-c7009e557578" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetRetirementObligation_019fd7b0-fb2a-713f-b1cf-524348f8f767" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetRetirementObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_AssetRetirementObligation_019fd7b0-fb2a-713f-b1cf-524348f8f767" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019fd7b0-fb2a-7b9e-9428-82d80bb2e731" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019fd7b0-fb2a-7b9e-9428-82d80bb2e731" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019fd7b0-fb2a-7517-8c23-7d096bacb881" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019fd7b0-fb2a-7517-8c23-7d096bacb881" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019fd7b0-fb2a-756f-b595-7a17403c2f0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019fd7b0-fb2a-756f-b595-7a17403c2f0b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_RemainingPerformanceObligationsCustomerContract_019fd7b0-fb2a-7c76-b4b4-2cb2063d5f36" xlink:href="mir-20260930.xsd#mir_RemainingPerformanceObligationsCustomerContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_mir_RemainingPerformanceObligationsCustomerContract_019fd7b0-fb2a-7c76-b4b4-2cb2063d5f36" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_019fd7b0-fb2a-78fb-96d1-40bd2a1dc013" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_019fd7b0-fb2a-78fb-96d1-40bd2a1dc013" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019fd7b0-fb2a-7d36-aa5d-6da707f6c222" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mir_SummaryOfSignificantAccountingPolicyLineItems_019fd7b0-fb2a-7558-9315-ac2e2bcdd92a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019fd7b0-fb2a-7d36-aa5d-6da707f6c222" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/BusinessCombinationsAcquisitionsandBusinessDisposalsNarrativeDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#BusinessCombinationsAcquisitionsandBusinessDisposalsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/BusinessCombinationsAcquisitionsandBusinessDisposalsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_019fd7b0-fb2a-71cc-b08b-9d0fef5c4902" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable_019fd7b0-fb2a-75d6-8416-408ce3039bae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_019fd7b0-fb2a-71cc-b08b-9d0fef5c4902" xlink:to="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable_019fd7b0-fb2a-75d6-8416-408ce3039bae" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fd7b0-fb2a-7c7e-b1a4-7db20349579f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable_019fd7b0-fb2a-75d6-8416-408ce3039bae" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fd7b0-fb2a-7c7e-b1a4-7db20349579f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fb2a-7c7e-b1a4-7db20349579f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd7b0-fb2a-7c7e-b1a4-7db20349579f" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fb2a-7c7e-b1a4-7db20349579f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fb2a-750d-a4a9-32285c688fb4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd7b0-fb2a-7c7e-b1a4-7db20349579f" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fb2a-750d-a4a9-32285c688fb4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_CertrecCorporationMember_019fd7b0-fb2a-7030-97f9-73c5cc4601b9" xlink:href="mir-20260930.xsd#mir_CertrecCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fb2a-750d-a4a9-32285c688fb4" xlink:to="loc_mir_CertrecCorporationMember_019fd7b0-fb2a-7030-97f9-73c5cc4601b9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ParagonCorporationMember_019fd7b0-fb2a-70ca-ae0f-e001ca26d8c0" xlink:href="mir-20260930.xsd#mir_ParagonCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fb2a-750d-a4a9-32285c688fb4" xlink:to="loc_mir_ParagonCorporationMember_019fd7b0-fb2a-70ca-ae0f-e001ca26d8c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fb2a-7c1c-ab6f-5209204da128" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable_019fd7b0-fb2a-75d6-8416-408ce3039bae" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fb2a-7c1c-ab6f-5209204da128" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fd7b0-fb2a-7c1c-ab6f-5209204da128_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fb2a-7c1c-ab6f-5209204da128" xlink:to="loc_us-gaap_SegmentDomain_019fd7b0-fb2a-7c1c-ab6f-5209204da128_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fd7b0-fb2a-7e65-b720-efdbf786013b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fb2a-7c1c-ab6f-5209204da128" xlink:to="loc_us-gaap_SegmentDomain_019fd7b0-fb2a-7e65-b720-efdbf786013b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_NuclearSafetySegmentMember_019fd7b0-fb2a-714a-89fe-c77dbb186720" xlink:href="mir-20260930.xsd#mir_NuclearSafetySegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fd7b0-fb2a-7e65-b720-efdbf786013b" xlink:to="loc_mir_NuclearSafetySegmentMember_019fd7b0-fb2a-714a-89fe-c77dbb186720" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_019fd7b0-fb2a-74fd-9db1-91ad0a97aaa1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_019fd7b0-fb2a-71cc-b08b-9d0fef5c4902" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_019fd7b0-fb2a-74fd-9db1-91ad0a97aaa1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019fd7b0-fb2a-79e9-ad8e-c9cab1e6eb8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_019fd7b0-fb2a-71cc-b08b-9d0fef5c4902" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019fd7b0-fb2a-79e9-ad8e-c9cab1e6eb8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_019fd7b0-fb2a-70f0-8a38-d6a7ed55e8c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_019fd7b0-fb2a-71cc-b08b-9d0fef5c4902" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_019fd7b0-fb2a-70f0-8a38-d6a7ed55e8c6" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/BusinessCombinationsAcquisitionsandBusinessDisposalsScheduleofFairValueofNetAssetsAcquiredDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#BusinessCombinationsAcquisitionsandBusinessDisposalsScheduleofFairValueofNetAssetsAcquiredDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/BusinessCombinationsAcquisitionsandBusinessDisposalsScheduleofFairValueofNetAssetsAcquiredDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019fd7b0-fb2a-778b-89c8-1e9cf28764b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fd7b0-fb2a-7a83-a77b-f2feb14b84c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd7b0-fb2a-778b-89c8-1e9cf28764b8" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fd7b0-fb2a-7a83-a77b-f2feb14b84c8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fd7b0-fb2a-7fa0-bdd9-ccd6e6e68407" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fd7b0-fb2a-7a83-a77b-f2feb14b84c8" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fd7b0-fb2a-7fa0-bdd9-ccd6e6e68407" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fb2a-7fa0-bdd9-ccd6e6e68407_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd7b0-fb2a-7fa0-bdd9-ccd6e6e68407" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fb2a-7fa0-bdd9-ccd6e6e68407_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fb2a-7472-b841-9865fd909f11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd7b0-fb2a-7fa0-bdd9-ccd6e6e68407" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fb2a-7472-b841-9865fd909f11" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_CertrecCorporationMember_019fd7b0-fb2a-79b9-a39b-8a0e2133d05e" xlink:href="mir-20260930.xsd#mir_CertrecCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fb2a-7472-b841-9865fd909f11" xlink:to="loc_mir_CertrecCorporationMember_019fd7b0-fb2a-79b9-a39b-8a0e2133d05e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ParagonCorporationMember_019fd7b0-fb2a-7408-9173-104983204376" xlink:href="mir-20260930.xsd#mir_ParagonCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fb2a-7472-b841-9865fd909f11" xlink:to="loc_mir_ParagonCorporationMember_019fd7b0-fb2a-7408-9173-104983204376" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fb2a-7f6f-acda-89160eebf667" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fd7b0-fb2a-7a83-a77b-f2feb14b84c8" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fb2a-7f6f-acda-89160eebf667" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fd7b0-fb2a-7f6f-acda-89160eebf667_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fb2a-7f6f-acda-89160eebf667" xlink:to="loc_us-gaap_SegmentDomain_019fd7b0-fb2a-7f6f-acda-89160eebf667_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fd7b0-fb2a-7313-8800-2e835ed18878" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fb2a-7f6f-acda-89160eebf667" xlink:to="loc_us-gaap_SegmentDomain_019fd7b0-fb2a-7313-8800-2e835ed18878" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_NuclearSafetySegmentMember_019fd7b0-fb2a-7494-85ce-8eec28721c9b" xlink:href="mir-20260930.xsd#mir_NuclearSafetySegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fd7b0-fb2a-7313-8800-2e835ed18878" xlink:to="loc_mir_NuclearSafetySegmentMember_019fd7b0-fb2a-7494-85ce-8eec28721c9b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd7b0-fb2a-78be-a9d3-eb2aa8846e89" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fd7b0-fb2a-7a83-a77b-f2feb14b84c8" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd7b0-fb2a-78be-a9d3-eb2aa8846e89" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd7b0-fb2a-78be-a9d3-eb2aa8846e89_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd7b0-fb2a-78be-a9d3-eb2aa8846e89" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd7b0-fb2a-78be-a9d3-eb2aa8846e89_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd7b0-fb2a-7d27-be3a-abc9904c5329" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd7b0-fb2a-78be-a9d3-eb2aa8846e89" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd7b0-fb2a-7d27-be3a-abc9904c5329" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_019fd7b0-fb2a-7864-a968-da02bbea0d1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd7b0-fb2a-7d27-be3a-abc9904c5329" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_019fd7b0-fb2a-7864-a968-da02bbea0d1f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_019fd7b0-fb2a-7ed7-bc26-50f1c6f0ce31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd7b0-fb2a-7d27-be3a-abc9904c5329" xlink:to="loc_us-gaap_CustomerRelationshipsMember_019fd7b0-fb2a-7ed7-bc26-50f1c6f0ce31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_019fd7b0-fb2a-7b13-9cb9-12083591fbea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd7b0-fb2a-7d27-be3a-abc9904c5329" xlink:to="loc_us-gaap_TradeNamesMember_019fd7b0-fb2a-7b13-9cb9-12083591fbea" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BacklogAndOtherMember_019fd7b0-fb2a-7372-afa3-2f9e61624376" xlink:href="mir-20260930.xsd#mir_BacklogAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd7b0-fb2a-7d27-be3a-abc9904c5329" xlink:to="loc_mir_BacklogAndOtherMember_019fd7b0-fb2a-7372-afa3-2f9e61624376" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019fd7b0-fb2a-774d-ba6f-627e2a7bd5b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fd7b0-fb2a-7a83-a77b-f2feb14b84c8" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019fd7b0-fb2a-774d-ba6f-627e2a7bd5b6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fd7b0-fb2a-774d-ba6f-627e2a7bd5b6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019fd7b0-fb2a-774d-ba6f-627e2a7bd5b6" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fd7b0-fb2a-774d-ba6f-627e2a7bd5b6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fd7b0-fb2a-71ba-9a5f-743465b08008" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019fd7b0-fb2a-774d-ba6f-627e2a7bd5b6" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fd7b0-fb2a-71ba-9a5f-743465b08008" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_019fd7b0-fb2a-74fa-aa23-bda3b22745a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fd7b0-fb2a-71ba-9a5f-743465b08008" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_019fd7b0-fb2a-74fa-aa23-bda3b22745a1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fd7b0-fb2a-7407-b63f-733eed27a8f1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fd7b0-fb2a-7a83-a77b-f2feb14b84c8" xlink:to="loc_srt_RangeAxis_019fd7b0-fb2a-7407-b63f-733eed27a8f1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd7b0-fb2a-7407-b63f-733eed27a8f1_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019fd7b0-fb2a-7407-b63f-733eed27a8f1" xlink:to="loc_srt_RangeMember_019fd7b0-fb2a-7407-b63f-733eed27a8f1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd7b0-fb2a-7849-bfff-7021130fad92" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019fd7b0-fb2a-7407-b63f-733eed27a8f1" xlink:to="loc_srt_RangeMember_019fd7b0-fb2a-7849-bfff-7021130fad92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019fd7b0-fb2a-7829-92ae-b7942491c2c8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd7b0-fb2a-7849-bfff-7021130fad92" xlink:to="loc_srt_MinimumMember_019fd7b0-fb2a-7829-92ae-b7942491c2c8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fd7b0-fb2a-7580-99d5-eb9afee639c2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd7b0-fb2a-7849-bfff-7021130fad92" xlink:to="loc_srt_MaximumMember_019fd7b0-fb2a-7580-99d5-eb9afee639c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationConsiderationTransferredAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd7b0-fb2a-778b-89c8-1e9cf28764b8" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019fd7b0-fb2a-7c16-8c5c-42161c30e36b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_us-gaap_Goodwill_019fd7b0-fb2a-7c16-8c5c-42161c30e36b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_019fd7b0-fb2a-7a5c-b1d1-2c65bfd78559" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GoodwillPurchaseAccountingAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_019fd7b0-fb2a-7a5c-b1d1-2c65bfd78559" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_019fd7b0-fb2a-7949-8e31-ed1448771c1b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_019fd7b0-fb2a-7949-8e31-ed1448771c1b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentIntangibles_019fd7b0-fb2a-725f-b26e-bb5f0e400513" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentIntangibles_019fd7b0-fb2a-725f-b26e-bb5f0e400513" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_019fd7b0-fb2a-7e94-98a8-f350dbf71e30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_019fd7b0-fb2a-7e94-98a8-f350dbf71e30" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentCash_019fd7b0-fb2a-7780-8b89-645c5a7655d0" xlink:href="mir-20260930.xsd#mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentCash_019fd7b0-fb2a-7780-8b89-645c5a7655d0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessCombinationRecognizedAssetAcquiredRestrictedCashCurrent_019fd7b0-fb2a-708c-af0b-c92cbc4d1dc6" xlink:href="mir-20260930.xsd#mir_BusinessCombinationRecognizedAssetAcquiredRestrictedCashCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_mir_BusinessCombinationRecognizedAssetAcquiredRestrictedCashCurrent_019fd7b0-fb2a-708c-af0b-c92cbc4d1dc6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentRestrictedCashCurrent_019fd7b0-fb2a-702c-9875-1954e3c183d7" xlink:href="mir-20260930.xsd#mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentRestrictedCashCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentRestrictedCashCurrent_019fd7b0-fb2a-702c-9875-1954e3c183d7" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_019fd7b0-fb2a-7dd4-9764-360ef5d253c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_019fd7b0-fb2a-7dd4-9764-360ef5d253c6" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccountsReceivableNet_019fd7b0-fb2a-73c0-b7a0-5b3316d06e64" xlink:href="mir-20260930.xsd#mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccountsReceivableNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccountsReceivableNet_019fd7b0-fb2a-73c0-b7a0-5b3316d06e64" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessCombinationRecognizedAssetAcquiredCostsInExcessOfBillings_019fd7b0-fb2a-7e8e-90f9-73afbac51bd2" xlink:href="mir-20260930.xsd#mir_BusinessCombinationRecognizedAssetAcquiredCostsInExcessOfBillings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_mir_BusinessCombinationRecognizedAssetAcquiredCostsInExcessOfBillings_019fd7b0-fb2a-7e8e-90f9-73afbac51bd2" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentCostsInExcessOfBillings_019fd7b0-fb2a-794a-87c4-f54a1f598a27" xlink:href="mir-20260930.xsd#mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentCostsInExcessOfBillings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentCostsInExcessOfBillings_019fd7b0-fb2a-794a-87c4-f54a1f598a27" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_019fd7b0-fb2a-78d8-8ad7-9c7e8958749b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_019fd7b0-fb2a-78d8-8ad7-9c7e8958749b" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentInventory_019fd7b0-fb2a-710a-94f8-2513ce32e3f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentInventory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentInventory_019fd7b0-fb2a-710a-94f8-2513ce32e3f3" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_019fd7b0-fb2a-7208-aa88-99bfde351dd5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_019fd7b0-fb2a-7208-aa88-99bfde351dd5" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentPrepaidExpensesAndOtherCurrentsAssets_019fd7b0-fb2a-71e0-ab44-6b990d69fa01" xlink:href="mir-20260930.xsd#mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentPrepaidExpensesAndOtherCurrentsAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentPrepaidExpensesAndOtherCurrentsAssets_019fd7b0-fb2a-71e0-ab44-6b990d69fa01" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_019fd7b0-fb2a-721f-9514-5a1941351d28" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_019fd7b0-fb2a-721f-9514-5a1941351d28" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentPropertyPlantAndEquipment_019fd7b0-fb2a-7165-80f2-5574ca1c43c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentPropertyPlantAndEquipment_019fd7b0-fb2a-7165-80f2-5574ca1c43c3" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_019fd7b0-fb2a-7958-81cf-d54c231dfc9b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_019fd7b0-fb2a-7958-81cf-d54c231dfc9b" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOtherAssetsNonCurrent_019fd7b0-fb2a-742b-8168-130cbeb839fb" xlink:href="mir-20260930.xsd#mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOtherAssetsNonCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOtherAssetsNonCurrent_019fd7b0-fb2a-742b-8168-130cbeb839fb" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_019fd7b0-fb2a-75ab-8c1c-367ea9169629" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_019fd7b0-fb2a-75ab-8c1c-367ea9169629" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccountsPayable_019fd7b0-fb2a-78d4-a63e-eadae25cc8b7" xlink:href="mir-20260930.xsd#mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccountsPayable_019fd7b0-fb2a-78d4-a63e-eadae25cc8b7" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesDeferredRevenue_019fd7b0-fb2a-7ff1-95f4-4ab773af3ec5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesDeferredRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesDeferredRevenue_019fd7b0-fb2a-7ff1-95f4-4ab773af3ec5" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredContractRevenue_019fd7b0-fb2a-7a46-8d87-007ff5fa31c0" xlink:href="mir-20260930.xsd#mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredContractRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredContractRevenue_019fd7b0-fb2a-7a46-8d87-007ff5fa31c0" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessCombinationRecognizedLiabilityAssumedAccruedLiabilitiesAndOtherLiabilitiesCurrent_019fd7b0-fb2a-7cca-853e-21d36cef11f2" xlink:href="mir-20260930.xsd#mir_BusinessCombinationRecognizedLiabilityAssumedAccruedLiabilitiesAndOtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_mir_BusinessCombinationRecognizedLiabilityAssumedAccruedLiabilitiesAndOtherLiabilitiesCurrent_019fd7b0-fb2a-7cca-853e-21d36cef11f2" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccruedExpensesAndOtherCurrentLiabilities_019fd7b0-fb2a-7a8e-8328-ba3dd95181cc" xlink:href="mir-20260930.xsd#mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccruedExpensesAndOtherCurrentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccruedExpensesAndOtherCurrentLiabilities_019fd7b0-fb2a-7a8e-8328-ba3dd95181cc" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_019fd7b0-fb2a-74ab-89fb-f3c6739a1e69" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_019fd7b0-fb2a-74ab-89fb-f3c6739a1e69" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredIncomeTaxesNonCurrent_019fd7b0-fb2a-7e39-b3b0-eb13a2e5f96e" xlink:href="mir-20260930.xsd#mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredIncomeTaxesNonCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredIncomeTaxesNonCurrent_019fd7b0-fb2a-7e39-b3b0-eb13a2e5f96e" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_019fd7b0-fb2a-79d1-aecc-85e9dbe0677c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_019fd7b0-fb2a-79d1-aecc-85e9dbe0677c" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOtherLiabilitiesNonCurrent_019fd7b0-fb2a-70e3-9a01-d9740123b098" xlink:href="mir-20260930.xsd#mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOtherLiabilitiesNonCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOtherLiabilitiesNonCurrent_019fd7b0-fb2a-70e3-9a01-d9740123b098" xlink:type="arc" order="30"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessCombinationRecognizedIdentifiableTangibleAssetsAcquiredAndLiabilitiesAssumedNet_019fd7b0-fb2a-7415-8577-1000afa29cae" xlink:href="mir-20260930.xsd#mir_BusinessCombinationRecognizedIdentifiableTangibleAssetsAcquiredAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_mir_BusinessCombinationRecognizedIdentifiableTangibleAssetsAcquiredAndLiabilitiesAssumedNet_019fd7b0-fb2a-7415-8577-1000afa29cae" xlink:type="arc" order="31"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentTangibleAssetsAcquired_019fd7b0-fb2a-7ac1-93af-4792fd787b1e" xlink:href="mir-20260930.xsd#mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentTangibleAssetsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentTangibleAssetsAcquired_019fd7b0-fb2a-7ac1-93af-4792fd787b1e" xlink:type="arc" order="32"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019fd7b0-fb2a-71e3-b932-309e5831ec11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019fd7b0-fb2a-71e3-b932-309e5831ec11" xlink:type="arc" order="33"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferred_019fd7b0-fb2a-7f9a-8ae5-5a5f4c278c97" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferred_019fd7b0-fb2a-7f9a-8ae5-5a5f4c278c97" xlink:type="arc" order="34"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAcquiredFromAcquisition_019fd7b0-fb2a-7ad8-8d56-57213c89c0ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAcquiredFromAcquisition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_us-gaap_CashAcquiredFromAcquisition_019fd7b0-fb2a-7ad8-8d56-57213c89c0ca" xlink:type="arc" order="35"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentCashAndRestrictedCashAcquired_019fd7b0-fb2a-7c64-9ac7-72e437b95d7d" xlink:href="mir-20260930.xsd#mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentCashAndRestrictedCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentCashAndRestrictedCashAcquired_019fd7b0-fb2a-7c64-9ac7-72e437b95d7d" xlink:type="arc" order="36"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_019fd7b0-fb2a-7004-b7ea-25c58e6d0c6f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_019fd7b0-fb2a-7004-b7ea-25c58e6d0c6f" xlink:type="arc" order="37"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentGAAPPurchaseConsiderationNetOfCashAcquired_019fd7b0-fb2a-71b5-bc1c-8a8203a7eb85" xlink:href="mir-20260930.xsd#mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentGAAPPurchaseConsiderationNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd7b0-fb2a-7e87-a5ad-a36197608262" xlink:to="loc_mir_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentGAAPPurchaseConsiderationNetOfCashAcquired_019fd7b0-fb2a-71b5-bc1c-8a8203a7eb85" xlink:type="arc" order="38"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_019fd7b0-fb2a-79f7-9119-8c9902119316" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd7b0-fb2a-778b-89c8-1e9cf28764b8" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_019fd7b0-fb2a-79f7-9119-8c9902119316" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/BusinessCombinationsAcquisitionsandBusinessDisposalsScheduleofBusinessAcquisitionProFormaInformationDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#BusinessCombinationsAcquisitionsandBusinessDisposalsScheduleofBusinessAcquisitionProFormaInformationDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/BusinessCombinationsAcquisitionsandBusinessDisposalsScheduleofBusinessAcquisitionProFormaInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019fd7b0-fb2a-7b0f-9e46-446624dedfcd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fd7b0-fb2a-7883-8053-a0c4ba425b72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd7b0-fb2a-7b0f-9e46-446624dedfcd" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fd7b0-fb2a-7883-8053-a0c4ba425b72" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fd7b0-fb2a-7571-ad2f-c628e441ba40" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fd7b0-fb2a-7883-8053-a0c4ba425b72" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fd7b0-fb2a-7571-ad2f-c628e441ba40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fb2a-7571-ad2f-c628e441ba40_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd7b0-fb2a-7571-ad2f-c628e441ba40" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fb2a-7571-ad2f-c628e441ba40_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fb2a-71ef-9fd4-f0189c96cd69" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd7b0-fb2a-7571-ad2f-c628e441ba40" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fb2a-71ef-9fd4-f0189c96cd69" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_CertrecCorporationMember_019fd7b0-fb2a-7db6-8a62-29c962c5a1e0" xlink:href="mir-20260930.xsd#mir_CertrecCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fb2a-71ef-9fd4-f0189c96cd69" xlink:to="loc_mir_CertrecCorporationMember_019fd7b0-fb2a-7db6-8a62-29c962c5a1e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_019fd7b0-fb2a-7b7c-b8fb-bb9ae1117c0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionsProFormaRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd7b0-fb2a-7b0f-9e46-446624dedfcd" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_019fd7b0-fb2a-7b7c-b8fb-bb9ae1117c0d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessAcquisitionsProFormaRevenueProfitLoss_019fd7b0-fb2a-7938-880b-3ae3828c7af3" xlink:href="mir-20260930.xsd#mir_BusinessAcquisitionsProFormaRevenueProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd7b0-fb2a-7b0f-9e46-446624dedfcd" xlink:to="loc_mir_BusinessAcquisitionsProFormaRevenueProfitLoss_019fd7b0-fb2a-7938-880b-3ae3828c7af3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_019fd7b0-fb2a-729b-80e4-cbfc37c97759" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd7b0-fb2a-7b0f-9e46-446624dedfcd" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_019fd7b0-fb2a-729b-80e4-cbfc37c97759" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/ContractsinProgressScheduleofUncompletedContractsDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#ContractsinProgressScheduleofUncompletedContractsDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/ContractsinProgressScheduleofUncompletedContractsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019fd7b0-fb2a-7a57-a45b-298239f2da3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019fd7b0-fb2a-716f-a8a3-b057ea36f0ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019fd7b0-fb2a-7a57-a45b-298239f2da3f" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019fd7b0-fb2a-716f-a8a3-b057ea36f0ae" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_019fd7b0-fb2a-75a9-b83b-ab93d960940d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019fd7b0-fb2a-716f-a8a3-b057ea36f0ae" xlink:to="loc_srt_MajorCustomersAxis_019fd7b0-fb2a-75a9-b83b-ab93d960940d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019fd7b0-fb2a-75a9-b83b-ab93d960940d_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_019fd7b0-fb2a-75a9-b83b-ab93d960940d" xlink:to="loc_srt_NameOfMajorCustomerDomain_019fd7b0-fb2a-75a9-b83b-ab93d960940d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019fd7b0-fb2a-7432-a426-bc9a9360d951" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_019fd7b0-fb2a-75a9-b83b-ab93d960940d" xlink:to="loc_srt_NameOfMajorCustomerDomain_019fd7b0-fb2a-7432-a426-bc9a9360d951" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_UncompletedContractsMember_019fd7b0-fb2a-7a21-b6e0-fcf9a374db50" xlink:href="mir-20260930.xsd#mir_UncompletedContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019fd7b0-fb2a-7432-a426-bc9a9360d951" xlink:to="loc_mir_UncompletedContractsMember_019fd7b0-fb2a-7a21-b6e0-fcf9a374db50" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNetCurrent_019fd7b0-fb2a-721d-b132-84433f28662c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerAssetNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019fd7b0-fb2a-7a57-a45b-298239f2da3f" xlink:to="loc_us-gaap_ContractWithCustomerAssetNetCurrent_019fd7b0-fb2a-721d-b132-84433f28662c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNetNoncurrent_019fd7b0-fb2a-7051-8845-d4ecaf02a395" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerAssetNetNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019fd7b0-fb2a-7a57-a45b-298239f2da3f" xlink:to="loc_us-gaap_ContractWithCustomerAssetNetNoncurrent_019fd7b0-fb2a-7051-8845-d4ecaf02a395" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019fd7b0-fb2a-7a4a-9c25-7f71b83f9518" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019fd7b0-fb2a-7a57-a45b-298239f2da3f" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019fd7b0-fb2a-7a4a-9c25-7f71b83f9518" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_019fd7b0-fb2a-75aa-8097-7a8705ebb3c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019fd7b0-fb2a-7a57-a45b-298239f2da3f" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_019fd7b0-fb2a-75aa-8097-7a8705ebb3c4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ContractWithCustomerAssetLiabilityNet_019fd7b0-fb2a-7cf5-919a-8d6c4a9f16d2" xlink:href="mir-20260930.xsd#mir_ContractWithCustomerAssetLiabilityNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019fd7b0-fb2a-7a57-a45b-298239f2da3f" xlink:to="loc_mir_ContractWithCustomerAssetLiabilityNet_019fd7b0-fb2a-7cf5-919a-8d6c4a9f16d2" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/PropertyPlantandEquipmentNetScheduleofPropertyPlantandEquipmentDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#PropertyPlantandEquipmentNetScheduleofPropertyPlantandEquipmentDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/PropertyPlantandEquipmentNetScheduleofPropertyPlantandEquipmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019fd7b0-fb2a-7533-a4cf-4cb82798c9a4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019fd7b0-fb2a-705e-b8ce-484d56fdf772" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019fd7b0-fb2a-7533-a4cf-4cb82798c9a4" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019fd7b0-fb2a-705e-b8ce-484d56fdf772" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fd7b0-fb2a-7d4d-92ab-1c608a6559b2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019fd7b0-fb2a-705e-b8ce-484d56fdf772" xlink:to="loc_srt_RangeAxis_019fd7b0-fb2a-7d4d-92ab-1c608a6559b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd7b0-fb2a-7d4d-92ab-1c608a6559b2_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019fd7b0-fb2a-7d4d-92ab-1c608a6559b2" xlink:to="loc_srt_RangeMember_019fd7b0-fb2a-7d4d-92ab-1c608a6559b2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd7b0-fb2a-7efe-8ee1-239fa884d08f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019fd7b0-fb2a-7d4d-92ab-1c608a6559b2" xlink:to="loc_srt_RangeMember_019fd7b0-fb2a-7efe-8ee1-239fa884d08f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019fd7b0-fb2a-78bc-8404-6a2717b702d3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd7b0-fb2a-7efe-8ee1-239fa884d08f" xlink:to="loc_srt_MinimumMember_019fd7b0-fb2a-78bc-8404-6a2717b702d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fd7b0-fb2a-7320-a86b-0ce45eff2bf4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd7b0-fb2a-7efe-8ee1-239fa884d08f" xlink:to="loc_srt_MaximumMember_019fd7b0-fb2a-7320-a86b-0ce45eff2bf4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019fd7b0-fb2a-7d40-9e49-270f4726b44c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019fd7b0-fb2a-705e-b8ce-484d56fdf772" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019fd7b0-fb2a-7d40-9e49-270f4726b44c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fd7b0-fb2a-7d40-9e49-270f4726b44c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019fd7b0-fb2a-7d40-9e49-270f4726b44c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fd7b0-fb2a-7d40-9e49-270f4726b44c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fd7b0-fb2a-7b7e-971a-d18678c08e1b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019fd7b0-fb2a-7d40-9e49-270f4726b44c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fd7b0-fb2a-7b7e-971a-d18678c08e1b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandBuildingsAndImprovementsMember_019fd7b0-fb2a-72d9-892d-fd4e3aa58866" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LandBuildingsAndImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fd7b0-fb2a-7b7e-971a-d18678c08e1b" xlink:to="loc_us-gaap_LandBuildingsAndImprovementsMember_019fd7b0-fb2a-72d9-892d-fd4e3aa58866" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MachineryAndEquipmentMember_019fd7b0-fb2a-7581-b685-ce906723e443" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MachineryAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fd7b0-fb2a-7b7e-971a-d18678c08e1b" xlink:to="loc_us-gaap_MachineryAndEquipmentMember_019fd7b0-fb2a-7581-b685-ce906723e443" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BadgesMember_019fd7b0-fb2a-7d49-adab-bedc5f134c68" xlink:href="mir-20260930.xsd#mir_BadgesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fd7b0-fb2a-7b7e-971a-d18678c08e1b" xlink:to="loc_mir_BadgesMember_019fd7b0-fb2a-7d49-adab-bedc5f134c68" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_FurnitureFixturesComputerEquipmentAndOtherMember_019fd7b0-fb2a-7c35-a16d-8136de0ad7aa" xlink:href="mir-20260930.xsd#mir_FurnitureFixturesComputerEquipmentAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fd7b0-fb2a-7b7e-971a-d18678c08e1b" xlink:to="loc_mir_FurnitureFixturesComputerEquipmentAndOtherMember_019fd7b0-fb2a-7c35-a16d-8136de0ad7aa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_019fd7b0-fb2a-7ac7-9222-d6733d0a58f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fd7b0-fb2a-7b7e-971a-d18678c08e1b" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_019fd7b0-fb2a-7ac7-9222-d6733d0a58f8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_019fd7b0-fb2a-7609-87b7-55c82b0dcb3e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fd7b0-fb2a-7b7e-971a-d18678c08e1b" xlink:to="loc_us-gaap_ConstructionInProgressMember_019fd7b0-fb2a-7609-87b7-55c82b0dcb3e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareDevelopmentMember_019fd7b0-fb2a-74bc-9b5d-876f1f038207" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SoftwareDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConstructionInProgressMember_019fd7b0-fb2a-7609-87b7-55c82b0dcb3e" xlink:to="loc_us-gaap_SoftwareDevelopmentMember_019fd7b0-fb2a-74bc-9b5d-876f1f038207" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_019fd7b0-fb2a-70d6-920b-572b8d597ea7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019fd7b0-fb2a-7533-a4cf-4cb82798c9a4" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_019fd7b0-fb2a-70d6-920b-572b8d597ea7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_019fd7b0-fb2a-724e-8996-1731781b1789" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019fd7b0-fb2a-7533-a4cf-4cb82798c9a4" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_019fd7b0-fb2a-724e-8996-1731781b1789" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019fd7b0-fb2a-7bb9-a3d9-f8d04d75255b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019fd7b0-fb2a-7533-a4cf-4cb82798c9a4" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019fd7b0-fb2a-7bb9-a3d9-f8d04d75255b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019fd7b0-fb2a-7e0c-8da4-e2290f0983e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019fd7b0-fb2a-7533-a4cf-4cb82798c9a4" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019fd7b0-fb2a-7e0c-8da4-e2290f0983e1" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/PropertyPlantandEquipmentNetScheduleofDepreciationExpenseDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#PropertyPlantandEquipmentNetScheduleofDepreciationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/PropertyPlantandEquipmentNetScheduleofDepreciationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019fd7b0-fb2a-731f-b8ed-3742f939f703" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019fd7b0-fb2a-7bd4-b967-a5c7f598c393" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019fd7b0-fb2a-731f-b8ed-3742f939f703" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019fd7b0-fb2a-7bd4-b967-a5c7f598c393" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019fd7b0-fb2a-7aa9-821c-74b4876a90f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019fd7b0-fb2a-7bd4-b967-a5c7f598c393" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019fd7b0-fb2a-7aa9-821c-74b4876a90f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_019fd7b0-fb2a-7d29-9b4f-156ef4a8f385" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019fd7b0-fb2a-731f-b8ed-3742f939f703" xlink:to="loc_us-gaap_Depreciation_019fd7b0-fb2a-7d29-9b4f-156ef4a8f385" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/PropertyPlantandEquipmentNetScheduleofDepreciationExpenseDetails_1" xlink:type="simple" xlink:href="mir-20260930.xsd#PropertyPlantandEquipmentNetScheduleofDepreciationExpenseDetails_1"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/PropertyPlantandEquipmentNetScheduleofDepreciationExpenseDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019fd7b0-fb2a-731f-b8ed-3742f939f703" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019fd7b0-fb2a-7bd4-b967-a5c7f598c393" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019fd7b0-fb2a-731f-b8ed-3742f939f703" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019fd7b0-fb2a-7bd4-b967-a5c7f598c393" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_019fd7b0-fb2a-7d29-9b4f-156ef4a8f385" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019fd7b0-fb2a-731f-b8ed-3742f939f703" xlink:to="loc_us-gaap_Depreciation_019fd7b0-fb2a-7d29-9b4f-156ef4a8f385" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/GoodwillandIntangibleAssetsScheduleofGoodwillDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#GoodwillandIntangibleAssetsScheduleofGoodwillDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/GoodwillandIntangibleAssetsScheduleofGoodwillDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_019fd7b0-fbc2-720a-9d0d-a52594fdd991" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_019fd7b0-fbc2-77f8-bb2f-731ad560fb31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_019fd7b0-fbc2-720a-9d0d-a52594fdd991" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_019fd7b0-fbc2-77f8-bb2f-731ad560fb31" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-701a-a655-24f1195a3827" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_019fd7b0-fbc2-77f8-bb2f-731ad560fb31" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-701a-a655-24f1195a3827" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-701a-a655-24f1195a3827_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-701a-a655-24f1195a3827" xlink:to="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-701a-a655-24f1195a3827_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-7ea0-b755-403981a543e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-701a-a655-24f1195a3827" xlink:to="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-7ea0-b755-403981a543e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_NuclearSafetySegmentMember_019fd7b0-fbc2-701d-8a62-0425e0bbaf3f" xlink:href="mir-20260930.xsd#mir_NuclearSafetySegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-7ea0-b755-403981a543e8" xlink:to="loc_mir_NuclearSafetySegmentMember_019fd7b0-fbc2-701d-8a62-0425e0bbaf3f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_MedicalSegmentMember_019fd7b0-fbc2-7c03-a9c8-757aea0180c8" xlink:href="mir-20260930.xsd#mir_MedicalSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-7ea0-b755-403981a543e8" xlink:to="loc_mir_MedicalSegmentMember_019fd7b0-fbc2-7c03-a9c8-757aea0180c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillRollForward_019fd7b0-fbc2-7a6b-ab37-b9083ea6eb07" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GoodwillRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_019fd7b0-fbc2-720a-9d0d-a52594fdd991" xlink:to="loc_us-gaap_GoodwillRollForward_019fd7b0-fbc2-7a6b-ab37-b9083ea6eb07" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019fd7b0-fbc2-7a4f-9ea2-c5e8b4b012a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_019fd7b0-fbc2-7a6b-ab37-b9083ea6eb07" xlink:to="loc_us-gaap_Goodwill_019fd7b0-fbc2-7a4f-9ea2-c5e8b4b012a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_019fd7b0-fbc2-7999-b788-b0f10390a5fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GoodwillPurchaseAccountingAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_019fd7b0-fbc2-7a6b-ab37-b9083ea6eb07" xlink:to="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_019fd7b0-fbc2-7999-b788-b0f10390a5fb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillForeignCurrencyTranslationGainLoss_019fd7b0-fbc2-7816-8930-631547093132" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GoodwillForeignCurrencyTranslationGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_019fd7b0-fbc2-7a6b-ab37-b9083ea6eb07" xlink:to="loc_us-gaap_GoodwillForeignCurrencyTranslationGainLoss_019fd7b0-fbc2-7816-8930-631547093132" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019fd7b0-fbc2-7195-94c6-e49e7658aeaf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillGross_019fd7b0-fbc2-7ae7-854c-d14c062d45e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GoodwillGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_019fd7b0-fbc2-720a-9d0d-a52594fdd991" xlink:to="loc_us-gaap_GoodwillGross_019fd7b0-fbc2-7ae7-854c-d14c062d45e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairedAccumulatedImpairmentLoss_019fd7b0-fbc2-76ca-a4b0-30d06f1686e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GoodwillImpairedAccumulatedImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_019fd7b0-fbc2-720a-9d0d-a52594fdd991" xlink:to="loc_us-gaap_GoodwillImpairedAccumulatedImpairmentLoss_019fd7b0-fbc2-76ca-a4b0-30d06f1686e9" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/GoodwillandIntangibleAssetsScheduleofFiniteLivedIntangibleAssetsDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#GoodwillandIntangibleAssetsScheduleofFiniteLivedIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/GoodwillandIntangibleAssetsScheduleofFiniteLivedIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019fd7b0-fbc2-7ee1-b4c3-64b0d5f706b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019fd7b0-fbc2-7d26-bc40-4b4623f4a596" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019fd7b0-fbc2-7ee1-b4c3-64b0d5f706b3" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019fd7b0-fbc2-7d26-bc40-4b4623f4a596" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fd7b0-fbc2-7138-bb22-79d019f812ba" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019fd7b0-fbc2-7d26-bc40-4b4623f4a596" xlink:to="loc_srt_RangeAxis_019fd7b0-fbc2-7138-bb22-79d019f812ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd7b0-fbc2-7138-bb22-79d019f812ba_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019fd7b0-fbc2-7138-bb22-79d019f812ba" xlink:to="loc_srt_RangeMember_019fd7b0-fbc2-7138-bb22-79d019f812ba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd7b0-fbc2-7435-a645-61a356f99b96" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019fd7b0-fbc2-7138-bb22-79d019f812ba" xlink:to="loc_srt_RangeMember_019fd7b0-fbc2-7435-a645-61a356f99b96" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019fd7b0-fbc2-7850-b31c-10718478cc42" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd7b0-fbc2-7435-a645-61a356f99b96" xlink:to="loc_srt_MinimumMember_019fd7b0-fbc2-7850-b31c-10718478cc42" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fd7b0-fbc2-7ce5-b1a6-276c897c8b2a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd7b0-fbc2-7435-a645-61a356f99b96" xlink:to="loc_srt_MaximumMember_019fd7b0-fbc2-7ce5-b1a6-276c897c8b2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd7b0-fbc2-7f47-b318-18a0fd97fd1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019fd7b0-fbc2-7d26-bc40-4b4623f4a596" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd7b0-fbc2-7f47-b318-18a0fd97fd1d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd7b0-fbc2-7f47-b318-18a0fd97fd1d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd7b0-fbc2-7f47-b318-18a0fd97fd1d" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd7b0-fbc2-7f47-b318-18a0fd97fd1d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd7b0-fbc2-7012-a364-b1603e037ba9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd7b0-fbc2-7f47-b318-18a0fd97fd1d" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd7b0-fbc2-7012-a364-b1603e037ba9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_019fd7b0-fbc2-73b2-8998-33e7f4d12fb5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd7b0-fbc2-7012-a364-b1603e037ba9" xlink:to="loc_us-gaap_CustomerRelationshipsMember_019fd7b0-fbc2-73b2-8998-33e7f4d12fb5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_DistributorRelationshipsMember_019fd7b0-fbc2-72d5-989a-8a87e9dd2904" xlink:href="mir-20260930.xsd#mir_DistributorRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd7b0-fbc2-7012-a364-b1603e037ba9" xlink:to="loc_mir_DistributorRelationshipsMember_019fd7b0-fbc2-72d5-989a-8a87e9dd2904" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_019fd7b0-fbc2-789f-94e6-f9561e608201" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd7b0-fbc2-7012-a364-b1603e037ba9" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_019fd7b0-fbc2-789f-94e6-f9561e608201" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_019fd7b0-fbc2-76eb-9888-a0d3f5744314" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd7b0-fbc2-7012-a364-b1603e037ba9" xlink:to="loc_us-gaap_TradeNamesMember_019fd7b0-fbc2-76eb-9888-a0d3f5744314" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_RemainingPerformanceObligationsAndOtherMember_019fd7b0-fbc2-7826-bc86-8708e17077cc" xlink:href="mir-20260930.xsd#mir_RemainingPerformanceObligationsAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd7b0-fbc2-7012-a364-b1603e037ba9" xlink:to="loc_mir_RemainingPerformanceObligationsAndOtherMember_019fd7b0-fbc2-7826-bc86-8708e17077cc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_019fd7b0-fbc2-7028-9f55-be499f8649d7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019fd7b0-fbc2-7ee1-b4c3-64b0d5f706b3" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_019fd7b0-fbc2-7028-9f55-be499f8649d7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019fd7b0-fbc2-7e02-a76a-cb32f04e1396" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019fd7b0-fbc2-7ee1-b4c3-64b0d5f706b3" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019fd7b0-fbc2-7e02-a76a-cb32f04e1396" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019fd7b0-fbc2-7275-b392-965cbe6fb277" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019fd7b0-fbc2-7ee1-b4c3-64b0d5f706b3" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019fd7b0-fbc2-7275-b392-965cbe6fb277" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019fd7b0-fbc2-7fe0-a119-18f9d7689111" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019fd7b0-fbc2-7ee1-b4c3-64b0d5f706b3" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019fd7b0-fbc2-7fe0-a119-18f9d7689111" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/GoodwillandIntangibleAssetsScheduleofFinitelivedIntangibleAssetsAmortizationExpenseDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#GoodwillandIntangibleAssetsScheduleofFinitelivedIntangibleAssetsAmortizationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/GoodwillandIntangibleAssetsScheduleofFinitelivedIntangibleAssetsAmortizationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019fd7b0-fbc2-77ee-83f0-aa0b6741aca0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019fd7b0-fbc2-7171-9c6b-f57012dee1a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019fd7b0-fbc2-77ee-83f0-aa0b6741aca0" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019fd7b0-fbc2-7171-9c6b-f57012dee1a5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019fd7b0-fbc2-72f2-ae8d-295265998b0f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019fd7b0-fbc2-7171-9c6b-f57012dee1a5" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019fd7b0-fbc2-72f2-ae8d-295265998b0f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_019fd7b0-fbc2-78ef-b0af-65fa53ab54f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019fd7b0-fbc2-77ee-83f0-aa0b6741aca0" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_019fd7b0-fbc2-78ef-b0af-65fa53ab54f4" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/GoodwillandIntangibleAssetsScheduleofFinitelivedIntangibleAssetsAmortizationExpenseDetails_1" xlink:type="simple" xlink:href="mir-20260930.xsd#GoodwillandIntangibleAssetsScheduleofFinitelivedIntangibleAssetsAmortizationExpenseDetails_1"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/GoodwillandIntangibleAssetsScheduleofFinitelivedIntangibleAssetsAmortizationExpenseDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019fd7b0-fbc2-77ee-83f0-aa0b6741aca0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019fd7b0-fbc2-7171-9c6b-f57012dee1a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019fd7b0-fbc2-77ee-83f0-aa0b6741aca0" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019fd7b0-fbc2-7171-9c6b-f57012dee1a5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_019fd7b0-fbc2-78ef-b0af-65fa53ab54f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019fd7b0-fbc2-77ee-83f0-aa0b6741aca0" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_019fd7b0-fbc2-78ef-b0af-65fa53ab54f4" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/BorrowingsScheduleofDebtDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#BorrowingsScheduleofDebtDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/BorrowingsScheduleofDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-79dc-8a22-4e2d8d7cf28a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019fd7b0-fbc2-7c61-8160-78ccc5c6fb84" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-79dc-8a22-4e2d8d7cf28a" xlink:to="loc_us-gaap_DebtInstrumentTable_019fd7b0-fbc2-7c61-8160-78ccc5c6fb84" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fbc2-784b-a2b9-978cf23e76e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fd7b0-fbc2-7c61-8160-78ccc5c6fb84" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fbc2-784b-a2b9-978cf23e76e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-784b-a2b9-978cf23e76e9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fbc2-784b-a2b9-978cf23e76e9" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-784b-a2b9-978cf23e76e9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-722c-9a83-448cdd9e232a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fbc2-784b-a2b9-978cf23e76e9" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-722c-9a83-448cdd9e232a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_TwoThousandAndTwentyOneCreditAgreementMember_019fd7b0-fbc2-70f0-8a50-a95573887432" xlink:href="mir-20260930.xsd#mir_TwoThousandAndTwentyOneCreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-722c-9a83-448cdd9e232a" xlink:to="loc_mir_TwoThousandAndTwentyOneCreditAgreementMember_019fd7b0-fbc2-70f0-8a50-a95573887432" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayableOtherPayablesMember_019fd7b0-fbc2-7608-9681-b9a3104ae102" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayableOtherPayablesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-722c-9a83-448cdd9e232a" xlink:to="loc_us-gaap_NotesPayableOtherPayablesMember_019fd7b0-fbc2-7608-9681-b9a3104ae102" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_019fd7b0-fbc2-768c-9e16-6190f1fb66ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-79dc-8a22-4e2d8d7cf28a" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_019fd7b0-fbc2-768c-9e16-6190f1fb66ef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_019fd7b0-fbc2-7fcf-8ef5-ca26238a84ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-79dc-8a22-4e2d8d7cf28a" xlink:to="loc_us-gaap_LongTermDebtCurrent_019fd7b0-fbc2-7fcf-8ef5-ca26238a84ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_019fd7b0-fbc2-7207-8d38-75543683eb9a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-79dc-8a22-4e2d8d7cf28a" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_019fd7b0-fbc2-7207-8d38-75543683eb9a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_019fd7b0-fbc2-731f-894b-a311e7397676" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-79dc-8a22-4e2d8d7cf28a" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_019fd7b0-fbc2-731f-894b-a311e7397676" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/BorrowingsNarrativeDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#BorrowingsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/BorrowingsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019fd7b0-fbc2-76d5-b277-3f282ce4fa23" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:to="loc_us-gaap_DebtInstrumentTable_019fd7b0-fbc2-76d5-b277-3f282ce4fa23" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-748f-8248-ececbc79bdc1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fd7b0-fbc2-76d5-b277-3f282ce4fa23" xlink:to="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-748f-8248-ececbc79bdc1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-748f-8248-ececbc79bdc1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-748f-8248-ececbc79bdc1" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-748f-8248-ececbc79bdc1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-7702-80f0-6bd13f1923cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-748f-8248-ececbc79bdc1" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-7702-80f0-6bd13f1923cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_TwoThousandAndTwentyOneCreditAgreementMember_019fd7b0-fbc2-74d7-a51c-9cd84ea6cdbb" xlink:href="mir-20260930.xsd#mir_TwoThousandAndTwentyOneCreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-7702-80f0-6bd13f1923cb" xlink:to="loc_mir_TwoThousandAndTwentyOneCreditAgreementMember_019fd7b0-fbc2-74d7-a51c-9cd84ea6cdbb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fbc2-7ebc-b2d0-7461e8723950" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fd7b0-fbc2-76d5-b277-3f282ce4fa23" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fbc2-7ebc-b2d0-7461e8723950" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-7ebc-b2d0-7461e8723950_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fbc2-7ebc-b2d0-7461e8723950" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-7ebc-b2d0-7461e8723950_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-7559-b4ed-059776e2afe5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fbc2-7ebc-b2d0-7461e8723950" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-7559-b4ed-059776e2afe5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019fd7b0-fbc2-788c-a280-d584c615969c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-7559-b4ed-059776e2afe5" xlink:to="loc_us-gaap_SecuredDebtMember_019fd7b0-fbc2-788c-a280-d584c615969c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019fd7b0-fbc2-7598-84a1-8518610549d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-7559-b4ed-059776e2afe5" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019fd7b0-fbc2-7598-84a1-8518610549d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_TermLoanFacilityMember_019fd7b0-fbc2-7398-95e4-7c646a901204" xlink:href="mir-20260930.xsd#mir_TermLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-7559-b4ed-059776e2afe5" xlink:to="loc_mir_TermLoanFacilityMember_019fd7b0-fbc2-7398-95e4-7c646a901204" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_019fd7b0-fbc2-7eaf-bc2a-9aebe69d2a53" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-7559-b4ed-059776e2afe5" xlink:to="loc_us-gaap_LetterOfCreditMember_019fd7b0-fbc2-7eaf-bc2a-9aebe69d2a53" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_019fd7b0-fbc2-73ae-9cd8-8983254e5bd1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fd7b0-fbc2-76d5-b277-3f282ce4fa23" xlink:to="loc_us-gaap_VariableRateAxis_019fd7b0-fbc2-73ae-9cd8-8983254e5bd1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019fd7b0-fbc2-73ae-9cd8-8983254e5bd1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_019fd7b0-fbc2-73ae-9cd8-8983254e5bd1" xlink:to="loc_us-gaap_VariableRateDomain_019fd7b0-fbc2-73ae-9cd8-8983254e5bd1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019fd7b0-fbc2-7ed6-94c3-6727cc52fadb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_019fd7b0-fbc2-73ae-9cd8-8983254e5bd1" xlink:to="loc_us-gaap_VariableRateDomain_019fd7b0-fbc2-7ed6-94c3-6727cc52fadb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_AdjustedSOFRMember_019fd7b0-fbc2-754a-b43b-ed028ebc74d4" xlink:href="mir-20260930.xsd#mir_AdjustedSOFRMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019fd7b0-fbc2-7ed6-94c3-6727cc52fadb" xlink:to="loc_mir_AdjustedSOFRMember_019fd7b0-fbc2-754a-b43b-ed028ebc74d4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_019fd7b0-fbc2-7c4a-a5b1-06a72f8fc572" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredOvernightFinancingRateSofrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019fd7b0-fbc2-7ed6-94c3-6727cc52fadb" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_019fd7b0-fbc2-7c4a-a5b1-06a72f8fc572" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fd7b0-fbc2-7e78-97e2-105da2350a82" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fd7b0-fbc2-76d5-b277-3f282ce4fa23" xlink:to="loc_srt_RangeAxis_019fd7b0-fbc2-7e78-97e2-105da2350a82" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd7b0-fbc2-7e78-97e2-105da2350a82_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019fd7b0-fbc2-7e78-97e2-105da2350a82" xlink:to="loc_srt_RangeMember_019fd7b0-fbc2-7e78-97e2-105da2350a82_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd7b0-fbc2-7d9e-9314-ff88063e4951" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019fd7b0-fbc2-7e78-97e2-105da2350a82" xlink:to="loc_srt_RangeMember_019fd7b0-fbc2-7d9e-9314-ff88063e4951" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019fd7b0-fbc2-7567-ba96-bf49e170ce83" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd7b0-fbc2-7d9e-9314-ff88063e4951" xlink:to="loc_srt_MinimumMember_019fd7b0-fbc2-7567-ba96-bf49e170ce83" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fd7b0-fbc2-7501-b13e-49b0606a0eb9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd7b0-fbc2-7d9e-9314-ff88063e4951" xlink:to="loc_srt_MaximumMember_019fd7b0-fbc2-7501-b13e-49b0606a0eb9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesSeniorNotes_019fd7b0-fbc2-7c09-8109-78e6a7ec6b2e" xlink:href="mir-20260930.xsd#mir_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesSeniorNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:to="loc_mir_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesSeniorNotes_019fd7b0-fbc2-7c09-8109-78e6a7ec6b2e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019fd7b0-fbc2-7122-9c06-a9ecad8d2a75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019fd7b0-fbc2-7122-9c06-a9ecad8d2a75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019fd7b0-fbc2-760d-a366-78830dbaac28" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:to="loc_us-gaap_LongTermDebt_019fd7b0-fbc2-760d-a366-78830dbaac28" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_019fd7b0-fbc2-76ef-ad10-a6a8ec6c9633" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_019fd7b0-fbc2-76ef-ad10-a6a8ec6c9633" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_LineOfCreditFacilityStepdownsCommitmentFeePercentage_019fd7b0-fbc2-753b-b655-5e94488b1f57" xlink:href="mir-20260930.xsd#mir_LineOfCreditFacilityStepdownsCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:to="loc_mir_LineOfCreditFacilityStepdownsCommitmentFeePercentage_019fd7b0-fbc2-753b-b655-5e94488b1f57" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_019fd7b0-fbc2-7aad-8bc0-a7eacc28ed87" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_019fd7b0-fbc2-7aad-8bc0-a7eacc28ed87" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_LeverageRatio_019fd7b0-fbc2-782c-876e-62eb3958d255" xlink:href="mir-20260930.xsd#mir_LeverageRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:to="loc_mir_LeverageRatio_019fd7b0-fbc2-782c-876e-62eb3958d255" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_RevolvingCreditFacilityOfExceedRevolvingCreditCommitmentPercentage_019fd7b0-fbc2-7c4e-a76a-1b21689b09f8" xlink:href="mir-20260930.xsd#mir_RevolvingCreditFacilityOfExceedRevolvingCreditCommitmentPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:to="loc_mir_RevolvingCreditFacilityOfExceedRevolvingCreditCommitmentPercentage_019fd7b0-fbc2-7c4e-a76a-1b21689b09f8" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtPercentageBearingVariableInterestRate_019fd7b0-fbc2-7732-b60d-5099cb5743f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtPercentageBearingVariableInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:to="loc_us-gaap_LongTermDebtPercentageBearingVariableInterestRate_019fd7b0-fbc2-7732-b60d-5099cb5743f5" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLongTermDebt_019fd7b0-fbc2-7b67-ae67-b0d39561099d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:to="loc_us-gaap_RepaymentsOfLongTermDebt_019fd7b0-fbc2-7b67-ae67-b0d39561099d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019fd7b0-fbc2-75ef-8d15-22b6b00b1a09" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019fd7b0-fbc2-75ef-8d15-22b6b00b1a09" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_AmortizationExpenseOfTheDeferredFinanceCost_019fd7b0-fbc2-7cfe-8c92-8c683d6770f5" xlink:href="mir-20260930.xsd#mir_AmortizationExpenseOfTheDeferredFinanceCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:to="loc_mir_AmortizationExpenseOfTheDeferredFinanceCost_019fd7b0-fbc2-7cfe-8c92-8c683d6770f5" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019fd7b0-fbc2-78ff-b414-c6500dad89ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019fd7b0-fbc2-78ff-b414-c6500dad89ff" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_DebtInstrumentOverdraftFacilitiesAmount_019fd7b0-fbc2-7d9d-b775-aa63ec67803f" xlink:href="mir-20260930.xsd#mir_DebtInstrumentOverdraftFacilitiesAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:to="loc_mir_DebtInstrumentOverdraftFacilitiesAmount_019fd7b0-fbc2-7d9d-b775-aa63ec67803f" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeReceivablesHeldForSaleAmount_019fd7b0-fbc2-782d-9225-b72962726197" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TradeReceivablesHeldForSaleAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:to="loc_us-gaap_TradeReceivablesHeldForSaleAmount_019fd7b0-fbc2-782d-9225-b72962726197" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity_019fd7b0-fbc2-7146-8207-6a2c8333ca21" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:to="loc_us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity_019fd7b0-fbc2-7146-8207-6a2c8333ca21" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLinesOfCredit_019fd7b0-fbc2-7c6e-b171-133124552e0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:to="loc_us-gaap_ProceedsFromLinesOfCredit_019fd7b0-fbc2-7c6e-b171-133124552e0c" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019fd7b0-fbc2-7177-abb1-0ee010fbee4f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019fd7b0-fbc2-7177-abb1-0ee010fbee4f" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCash_019fd7b0-fbc2-74c5-bd45-abfca4c1a98e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-750e-8977-84f4ce29484e" xlink:to="loc_us-gaap_RestrictedCash_019fd7b0-fbc2-74c5-bd45-abfca4c1a98e" xlink:type="arc" order="18"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/BorrowingsScheduleofContractualPrincipalPaymentsDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#BorrowingsScheduleofContractualPrincipalPaymentsDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/BorrowingsScheduleofContractualPrincipalPaymentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-7a57-8571-ecc966ee8d47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019fd7b0-fbc2-7f37-8d46-e2ae88fc0906" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-7a57-8571-ecc966ee8d47" xlink:to="loc_us-gaap_DebtInstrumentTable_019fd7b0-fbc2-7f37-8d46-e2ae88fc0906" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-794d-838e-a21226831a00" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fd7b0-fbc2-7f37-8d46-e2ae88fc0906" xlink:to="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-794d-838e-a21226831a00" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-794d-838e-a21226831a00_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-794d-838e-a21226831a00" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-794d-838e-a21226831a00_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-7083-9414-be9c8fe31fc3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-794d-838e-a21226831a00" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-7083-9414-be9c8fe31fc3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_DebtExcludingConvertibleDebtMember_019fd7b0-fbc2-7206-ba2a-939bbbc5fad2" xlink:href="mir-20260930.xsd#mir_DebtExcludingConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-7083-9414-be9c8fe31fc3" xlink:to="loc_mir_DebtExcludingConvertibleDebtMember_019fd7b0-fbc2-7206-ba2a-939bbbc5fad2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtByMaturityAbstract_01a040f5-7b87-70a1-92db-e27c0d0d5b81" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtByMaturityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd7b0-fbc2-7a57-8571-ecc966ee8d47" xlink:to="loc_us-gaap_LongTermDebtByMaturityAbstract_01a040f5-7b87-70a1-92db-e27c0d0d5b81" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalRemainderOfFiscalYear_019fd7b0-fbc2-7374-a541-954d4a7cb5b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_01a040f5-7b87-70a1-92db-e27c0d0d5b81" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalRemainderOfFiscalYear_019fd7b0-fbc2-7374-a541-954d4a7cb5b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths_019fd7b0-fbc2-7a71-bd3a-9ee5e2cbc3cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_01a040f5-7b87-70a1-92db-e27c0d0d5b81" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths_019fd7b0-fbc2-7a71-bd3a-9ee5e2cbc3cb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_019fd7b0-fbc2-7f5f-a868-301f0bf4bb52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_01a040f5-7b87-70a1-92db-e27c0d0d5b81" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_019fd7b0-fbc2-7f5f-a868-301f0bf4bb52" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_019fd7b0-fbc2-7ed7-8d20-c977d85c24f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_01a040f5-7b87-70a1-92db-e27c0d0d5b81" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_019fd7b0-fbc2-7ed7-8d20-c977d85c24f9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_019fd7b0-fbc2-7cd4-b0e3-69514bb52408" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_01a040f5-7b87-70a1-92db-e27c0d0d5b81" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_019fd7b0-fbc2-7cd4-b0e3-69514bb52408" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_LongTermDebtMaturityAfterYearFour_019fd7b0-fbc2-7c06-8ad8-b8b34ea9662f" xlink:href="mir-20260930.xsd#mir_LongTermDebtMaturityAfterYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_01a040f5-7b87-70a1-92db-e27c0d0d5b81" xlink:to="loc_mir_LongTermDebtMaturityAfterYearFour_019fd7b0-fbc2-7c06-8ad8-b8b34ea9662f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_019fd7b0-fbc2-7eb9-be4f-54a4f7fffff1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_01a040f5-7b87-70a1-92db-e27c0d0d5b81" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_019fd7b0-fbc2-7eb9-be4f-54a4f7fffff1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet_019fd7b0-fbc2-7a3e-a9a2-cd7fb05223c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_01a040f5-7b87-70a1-92db-e27c0d0d5b81" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet_019fd7b0-fbc2-7a3e-a9a2-cd7fb05223c7" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019fd7b0-fbc2-715d-9855-84bb7120190a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_01a040f5-7b87-70a1-92db-e27c0d0d5b81" xlink:to="loc_us-gaap_LongTermDebt_019fd7b0-fbc2-715d-9855-84bb7120190a" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/ConvertibleDebtScheduleofConvertibleDebtDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#ConvertibleDebtScheduleofConvertibleDebtDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/ConvertibleDebtScheduleofConvertibleDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-722f-8fa7-50056af6cd82" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionTable_019fd7b0-fbc2-7407-a750-70586b2ce48c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-722f-8fa7-50056af6cd82" xlink:to="loc_us-gaap_DebtInstrumentRedemptionTable_019fd7b0-fbc2-7407-a750-70586b2ce48c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fbc2-7221-aa9b-839fbcfed2d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentRedemptionTable_019fd7b0-fbc2-7407-a750-70586b2ce48c" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fbc2-7221-aa9b-839fbcfed2d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-7221-aa9b-839fbcfed2d2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fbc2-7221-aa9b-839fbcfed2d2" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-7221-aa9b-839fbcfed2d2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-788e-90a8-99023eb002e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fbc2-7221-aa9b-839fbcfed2d2" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-788e-90a8-99023eb002e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_019fd7b0-fbc2-712c-860d-a4a380eae904" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-788e-90a8-99023eb002e2" xlink:to="loc_us-gaap_ConvertibleDebtMember_019fd7b0-fbc2-712c-860d-a4a380eae904" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-76d9-b68a-c0532e4196dd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentRedemptionTable_019fd7b0-fbc2-7407-a750-70586b2ce48c" xlink:to="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-76d9-b68a-c0532e4196dd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-76d9-b68a-c0532e4196dd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-76d9-b68a-c0532e4196dd" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-76d9-b68a-c0532e4196dd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-749c-95d7-869c4fcabec7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-76d9-b68a-c0532e4196dd" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-749c-95d7-869c4fcabec7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ConvertibleSeniorNotesDue2030NotesMember_019fd7b0-fbc2-775e-9d3b-3dd8c2635f7b" xlink:href="mir-20260930.xsd#mir_ConvertibleSeniorNotesDue2030NotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-749c-95d7-869c4fcabec7" xlink:to="loc_mir_ConvertibleSeniorNotesDue2030NotesMember_019fd7b0-fbc2-775e-9d3b-3dd8c2635f7b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ConvertibleSeniorNotesDue2031NotesMember_019fd7b0-fbc2-773c-966f-9333a2245bc0" xlink:href="mir-20260930.xsd#mir_ConvertibleSeniorNotesDue2031NotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-749c-95d7-869c4fcabec7" xlink:to="loc_mir_ConvertibleSeniorNotesDue2031NotesMember_019fd7b0-fbc2-773c-966f-9333a2245bc0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtCurrent_019fd7b0-fbc2-78ff-827e-d32c539856d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-722f-8fa7-50056af6cd82" xlink:to="loc_us-gaap_ConvertibleDebtCurrent_019fd7b0-fbc2-78ff-827e-d32c539856d8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNoncurrentNet_019fd7b0-fbc2-76d6-bde2-606ce8559c83" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredFinanceCostsNoncurrentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-722f-8fa7-50056af6cd82" xlink:to="loc_us-gaap_DeferredFinanceCostsNoncurrentNet_019fd7b0-fbc2-76d6-bde2-606ce8559c83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebt_019fd7b0-fbc2-78f7-9d8b-acfb65eeabd8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-722f-8fa7-50056af6cd82" xlink:to="loc_us-gaap_ConvertibleDebt_019fd7b0-fbc2-78f7-9d8b-acfb65eeabd8" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/ConvertibleDebtNarrativeDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#ConvertibleDebtNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/ConvertibleDebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionTable_019fd7b0-fbc2-7709-9ae5-4b077c879b56" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_us-gaap_DebtInstrumentRedemptionTable_019fd7b0-fbc2-7709-9ae5-4b077c879b56" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-761a-8efa-640987899a6e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentRedemptionTable_019fd7b0-fbc2-7709-9ae5-4b077c879b56" xlink:to="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-761a-8efa-640987899a6e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-761a-8efa-640987899a6e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-761a-8efa-640987899a6e" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-761a-8efa-640987899a6e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-7a13-b5ca-3a5b68041e89" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-761a-8efa-640987899a6e" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-7a13-b5ca-3a5b68041e89" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ConvertibleSeniorNotesDue2030NotesMember_019fd7b0-fbc2-7b35-8e13-861adab6945b" xlink:href="mir-20260930.xsd#mir_ConvertibleSeniorNotesDue2030NotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-7a13-b5ca-3a5b68041e89" xlink:to="loc_mir_ConvertibleSeniorNotesDue2030NotesMember_019fd7b0-fbc2-7b35-8e13-861adab6945b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ConvertibleSeniorNotesDue2031NotesMember_019fd7b0-fbc2-79e0-857d-d0e5526e3c04" xlink:href="mir-20260930.xsd#mir_ConvertibleSeniorNotesDue2031NotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-7a13-b5ca-3a5b68041e89" xlink:to="loc_mir_ConvertibleSeniorNotesDue2031NotesMember_019fd7b0-fbc2-79e0-857d-d0e5526e3c04" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CallOptionMember_019fd7b0-fbc2-717a-9d19-813379ee9fc2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CallOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-7a13-b5ca-3a5b68041e89" xlink:to="loc_us-gaap_CallOptionMember_019fd7b0-fbc2-717a-9d19-813379ee9fc2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fbc2-7e2d-8c09-c367d444125f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentRedemptionTable_019fd7b0-fbc2-7709-9ae5-4b077c879b56" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fbc2-7e2d-8c09-c367d444125f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-7e2d-8c09-c367d444125f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fbc2-7e2d-8c09-c367d444125f" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-7e2d-8c09-c367d444125f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-73aa-a3ad-c0f1ee82230e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fbc2-7e2d-8c09-c367d444125f" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-73aa-a3ad-c0f1ee82230e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_019fd7b0-fbc2-75c1-8584-56c11774994d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-73aa-a3ad-c0f1ee82230e" xlink:to="loc_us-gaap_ConvertibleDebtMember_019fd7b0-fbc2-75c1-8584-56c11774994d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fbc2-7631-884c-ef2a9a88e7e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentRedemptionTable_019fd7b0-fbc2-7709-9ae5-4b077c879b56" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fbc2-7631-884c-ef2a9a88e7e6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-7631-884c-ef2a9a88e7e6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fbc2-7631-884c-ef2a9a88e7e6" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-7631-884c-ef2a9a88e7e6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-743a-b78c-7463e157f013" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fbc2-7631-884c-ef2a9a88e7e6" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-743a-b78c-7463e157f013" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019fd7b0-fbc2-764a-b371-448f6f990e22" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-743a-b78c-7463e157f013" xlink:to="loc_us-gaap_CommonClassAMember_019fd7b0-fbc2-764a-b371-448f6f990e22" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_019fd7b0-fbc2-789b-8d84-9baf4195eabe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentRedemptionTable_019fd7b0-fbc2-7709-9ae5-4b077c879b56" xlink:to="loc_us-gaap_TypeOfArrangementAxis_019fd7b0-fbc2-789b-8d84-9baf4195eabe" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fd7b0-fbc2-789b-8d84-9baf4195eabe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019fd7b0-fbc2-789b-8d84-9baf4195eabe" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fd7b0-fbc2-789b-8d84-9baf4195eabe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fd7b0-fbc2-7258-96c3-e75e204cf884" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019fd7b0-fbc2-789b-8d84-9baf4195eabe" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fd7b0-fbc2-7258-96c3-e75e204cf884" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_PurchaseAgreementMember_019fd7b0-fbc2-7b15-a712-3dc8101eeeae" xlink:href="mir-20260930.xsd#mir_PurchaseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fd7b0-fbc2-7258-96c3-e75e204cf884" xlink:to="loc_mir_PurchaseAgreementMember_019fd7b0-fbc2-7b15-a712-3dc8101eeeae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019fd7b0-fbc2-751e-8606-4bbf84ef80b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019fd7b0-fbc2-751e-8606-4bbf84ef80b5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019fd7b0-fbc2-7b5a-b5de-984e78f8e304" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019fd7b0-fbc2-7b5a-b5de-984e78f8e304" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_019fd7b0-fbc2-78b2-a9bf-128ccdcef6d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentConvertibleConversionRatio1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_019fd7b0-fbc2-78b2-a9bf-128ccdcef6d6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_DebtInstrumentPrincipalAmountForTradingPricePerNote_019fd7b0-fbc2-7ce4-8bdf-4df31f878519" xlink:href="mir-20260930.xsd#mir_DebtInstrumentPrincipalAmountForTradingPricePerNote"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_mir_DebtInstrumentPrincipalAmountForTradingPricePerNote_019fd7b0-fbc2-7ce4-8bdf-4df31f878519" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_019fd7b0-fbc2-76c6-af49-2d66b6625ccc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_019fd7b0-fbc2-76c6-af49-2d66b6625ccc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_DebtInstrumentConvertibleConversionPremium_019fd7b0-fbc2-77a4-8eff-6c6afe5e8daf" xlink:href="mir-20260930.xsd#mir_DebtInstrumentConvertibleConversionPremium"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_mir_DebtInstrumentConvertibleConversionPremium_019fd7b0-fbc2-77a4-8eff-6c6afe5e8daf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharePrice_019fd7b0-fbc2-7049-9935-3273f2ce7664" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_us-gaap_SharePrice_019fd7b0-fbc2-7049-9935-3273f2ce7664" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_019fd7b0-fbc2-72e1-aacb-09ee64a973da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionPricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_019fd7b0-fbc2-72e1-aacb-09ee64a973da" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_019fd7b0-fbc2-7643-a72a-aac21469f02e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_019fd7b0-fbc2-7643-a72a-aac21469f02e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_019fd7b0-fbc2-7db7-95fe-4d95948dcc42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentConvertibleThresholdTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_019fd7b0-fbc2-7db7-95fe-4d95948dcc42" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_019fd7b0-fbc2-75e4-89ac-75e3727af064" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_019fd7b0-fbc2-75e4-89ac-75e3727af064" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_DebtInstrumentRedemptionFaceAmountOfNotesThatMustBeOutstanding_019fd7b0-fbc2-781d-a499-962dc7e90ee3" xlink:href="mir-20260930.xsd#mir_DebtInstrumentRedemptionFaceAmountOfNotesThatMustBeOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_mir_DebtInstrumentRedemptionFaceAmountOfNotesThatMustBeOutstanding_019fd7b0-fbc2-781d-a499-962dc7e90ee3" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_DebtInstrumentConvertibleBusinessDays_019fd7b0-fbc2-7a88-b696-494029c442ff" xlink:href="mir-20260930.xsd#mir_DebtInstrumentConvertibleBusinessDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_mir_DebtInstrumentConvertibleBusinessDays_019fd7b0-fbc2-7a88-b696-494029c442ff" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_DebtInstrumentConvertibleConsecutiveTradingDays_019fd7b0-fbc2-7908-9a5d-f75f536add77" xlink:href="mir-20260930.xsd#mir_DebtInstrumentConvertibleConsecutiveTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_mir_DebtInstrumentConvertibleConsecutiveTradingDays_019fd7b0-fbc2-7908-9a5d-f75f536add77" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_DebtInstrumentConvertibleMaximumPercentageOfStockPriceTrigger_019fd7b0-fbc2-795a-90cc-7e0360824845" xlink:href="mir-20260930.xsd#mir_DebtInstrumentConvertibleMaximumPercentageOfStockPriceTrigger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_mir_DebtInstrumentConvertibleMaximumPercentageOfStockPriceTrigger_019fd7b0-fbc2-795a-90cc-7e0360824845" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_EquityPurchaseAgreementCommitment_019fd7b0-fbc2-7e0e-8740-be174ead598c" xlink:href="mir-20260930.xsd#mir_EquityPurchaseAgreementCommitment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_mir_EquityPurchaseAgreementCommitment_019fd7b0-fbc2-7e0e-8740-be174ead598c" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsGross_019fd7b0-fbc2-713a-9aee-7c005b03dba5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredFinanceCostsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_us-gaap_DeferredFinanceCostsGross_019fd7b0-fbc2-713a-9aee-7c005b03dba5" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_019fd7b0-fbc2-73d5-99e5-4252eb8df400" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_us-gaap_InterestExpense_019fd7b0-fbc2-73d5-99e5-4252eb8df400" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019fd7b0-fbc2-704c-a577-b6f2f034b16f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019fd7b0-fbc2-704c-a577-b6f2f034b16f" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_PremiumRecognizedOnCappedCallTransactionsPercent_019fd7b0-fbc2-74e4-86da-9b42d34c599d" xlink:href="mir-20260930.xsd#mir_PremiumRecognizedOnCappedCallTransactionsPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_mir_PremiumRecognizedOnCappedCallTransactionsPercent_019fd7b0-fbc2-74e4-86da-9b42d34c599d" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_PurchasesOfCappedCallsRelatedToConvertibleSeniorNotes_019fd7b0-fbc2-73a3-bd67-c5896d555bdc" xlink:href="mir-20260930.xsd#mir_PurchasesOfCappedCallsRelatedToConvertibleSeniorNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7a55-99b7-d25a010b3e3f" xlink:to="loc_mir_PurchasesOfCappedCallsRelatedToConvertibleSeniorNotes_019fd7b0-fbc2-73a3-bd67-c5896d555bdc" xlink:type="arc" order="20"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/ConvertibleDebtScheduleofFutureMaturitiesoftheNotesDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#ConvertibleDebtScheduleofFutureMaturitiesoftheNotesDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/ConvertibleDebtScheduleofFutureMaturitiesoftheNotesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7d7b-a5b9-f780d731522a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionTable_019fd7b0-fbc2-7b9c-b4d7-40dd17aede7a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7d7b-a5b9-f780d731522a" xlink:to="loc_us-gaap_DebtInstrumentRedemptionTable_019fd7b0-fbc2-7b9c-b4d7-40dd17aede7a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-763b-a757-a569653c8626" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentRedemptionTable_019fd7b0-fbc2-7b9c-b4d7-40dd17aede7a" xlink:to="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-763b-a757-a569653c8626" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-763b-a757-a569653c8626_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-763b-a757-a569653c8626" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-763b-a757-a569653c8626_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-7107-a525-b98a1d881663" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-763b-a757-a569653c8626" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-7107-a525-b98a1d881663" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ConvertibleSeniorNotesDue2030And2031NotesMember_019fd7b0-fbc2-7d18-bda4-e20aabae0168" xlink:href="mir-20260930.xsd#mir_ConvertibleSeniorNotesDue2030And2031NotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-7107-a525-b98a1d881663" xlink:to="loc_mir_ConvertibleSeniorNotesDue2030And2031NotesMember_019fd7b0-fbc2-7d18-bda4-e20aabae0168" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalRemainderOfFiscalYear_019fd7b0-fbc2-752a-ba39-8374b3881519" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7d7b-a5b9-f780d731522a" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalRemainderOfFiscalYear_019fd7b0-fbc2-752a-ba39-8374b3881519" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtByMaturityAbstract_01a040f3-ff6b-75f8-b3cd-eb7e4300706a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtByMaturityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionLineItems_019fd7b0-fbc2-7d7b-a5b9-f780d731522a" xlink:to="loc_us-gaap_LongTermDebtByMaturityAbstract_01a040f3-ff6b-75f8-b3cd-eb7e4300706a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths_019fd7b0-fbc2-7163-8163-f1757dae4e8c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_01a040f3-ff6b-75f8-b3cd-eb7e4300706a" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths_019fd7b0-fbc2-7163-8163-f1757dae4e8c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_019fd7b0-fbc2-7767-ac8c-a8ae66648034" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_01a040f3-ff6b-75f8-b3cd-eb7e4300706a" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_019fd7b0-fbc2-7767-ac8c-a8ae66648034" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_019fd7b0-fbc2-763e-bcdd-346ee0f785a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_01a040f3-ff6b-75f8-b3cd-eb7e4300706a" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_019fd7b0-fbc2-763e-bcdd-346ee0f785a6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_019fd7b0-fbc2-786c-8ea7-b5ebd54386bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_01a040f3-ff6b-75f8-b3cd-eb7e4300706a" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_019fd7b0-fbc2-786c-8ea7-b5ebd54386bc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_LongTermDebtMaturityAfterYearFour_019fd7b0-fbc2-78f2-9b67-eb721965093b" xlink:href="mir-20260930.xsd#mir_LongTermDebtMaturityAfterYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_01a040f3-ff6b-75f8-b3cd-eb7e4300706a" xlink:to="loc_mir_LongTermDebtMaturityAfterYearFour_019fd7b0-fbc2-78f2-9b67-eb721965093b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebt_019fd7b0-fbc2-7ebc-b5ce-d2fe3751a81a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_01a040f3-ff6b-75f8-b3cd-eb7e4300706a" xlink:to="loc_us-gaap_ConvertibleDebt_019fd7b0-fbc2-7ebc-b5ce-d2fe3751a81a" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/LeasedAssetsNarrativeDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#LeasedAssetsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/LeasedAssetsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_019fd7b0-fbc2-7e6f-8c11-4e0e0c9592df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_019fd7b0-fbc2-79b9-a1cc-9bfc0c7fbf78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019fd7b0-fbc2-7e6f-8c11-4e0e0c9592df" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_019fd7b0-fbc2-79b9-a1cc-9bfc0c7fbf78" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fd7b0-fbc2-767d-b248-0d0f4a01c172" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_019fd7b0-fbc2-79b9-a1cc-9bfc0c7fbf78" xlink:to="loc_srt_RangeAxis_019fd7b0-fbc2-767d-b248-0d0f4a01c172" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd7b0-fbc2-767d-b248-0d0f4a01c172_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019fd7b0-fbc2-767d-b248-0d0f4a01c172" xlink:to="loc_srt_RangeMember_019fd7b0-fbc2-767d-b248-0d0f4a01c172_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd7b0-fbc2-763b-a700-13a75f7f59ce" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019fd7b0-fbc2-767d-b248-0d0f4a01c172" xlink:to="loc_srt_RangeMember_019fd7b0-fbc2-763b-a700-13a75f7f59ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019fd7b0-fbc2-70ef-a521-6ee12f505e4e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd7b0-fbc2-763b-a700-13a75f7f59ce" xlink:to="loc_srt_MinimumMember_019fd7b0-fbc2-70ef-a521-6ee12f505e4e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fd7b0-fbc2-7e66-9ec6-5b70389b9ffc" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd7b0-fbc2-763b-a700-13a75f7f59ce" xlink:to="loc_srt_MaximumMember_019fd7b0-fbc2-7e66-9ec6-5b70389b9ffc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_019fd7b0-fbc2-73cc-ac57-afa335327479" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeOperatingLeaseRemainingLeaseTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019fd7b0-fbc2-7e6f-8c11-4e0e0c9592df" xlink:to="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_019fd7b0-fbc2-73cc-ac57-afa335327479" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_019fd7b0-fbc2-796d-9071-6669373fd0ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeOperatingLeaseRenewalTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019fd7b0-fbc2-7e6f-8c11-4e0e0c9592df" xlink:to="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_019fd7b0-fbc2-796d-9071-6669373fd0ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseCost_019fd7b0-fbc2-7e36-9afe-b93b5be0246f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019fd7b0-fbc2-7e6f-8c11-4e0e0c9592df" xlink:to="loc_us-gaap_OperatingLeaseCost_019fd7b0-fbc2-7e36-9afe-b93b5be0246f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeasePayments_019fd7b0-fbc2-7f3d-9315-b59c659cac7b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeasePayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019fd7b0-fbc2-7e6f-8c11-4e0e0c9592df" xlink:to="loc_us-gaap_OperatingLeasePayments_019fd7b0-fbc2-7f3d-9315-b59c659cac7b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_019fd7b0-fbc2-7659-a158-413e7b0af6c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019fd7b0-fbc2-7e6f-8c11-4e0e0c9592df" xlink:to="loc_us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_019fd7b0-fbc2-7659-a158-413e7b0af6c7" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/StockBasedCompensationDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#StockBasedCompensationDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/StockBasedCompensationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fd7b0-fbc2-76e0-b574-8a826d449d5f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fd7b0-fbc2-7c37-98d9-96755dfc6a89" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fd7b0-fbc2-76e0-b574-8a826d449d5f" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fd7b0-fbc2-7c37-98d9-96755dfc6a89" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019fd7b0-fbc2-7b59-892c-ad0412c119c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fd7b0-fbc2-7c37-98d9-96755dfc6a89" xlink:to="loc_us-gaap_PlanNameAxis_019fd7b0-fbc2-7b59-892c-ad0412c119c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019fd7b0-fbc2-7b59-892c-ad0412c119c1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019fd7b0-fbc2-7b59-892c-ad0412c119c1" xlink:to="loc_us-gaap_PlanNameDomain_019fd7b0-fbc2-7b59-892c-ad0412c119c1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019fd7b0-fbc2-77a5-a348-8192ac715ba7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019fd7b0-fbc2-7b59-892c-ad0412c119c1" xlink:to="loc_us-gaap_PlanNameDomain_019fd7b0-fbc2-77a5-a348-8192ac715ba7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_A2021OmnibusIncentivePlanMember_019fd7b0-fbc2-71d8-9616-11dd9011c77a" xlink:href="mir-20260930.xsd#mir_A2021OmnibusIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019fd7b0-fbc2-77a5-a348-8192ac715ba7" xlink:to="loc_mir_A2021OmnibusIncentivePlanMember_019fd7b0-fbc2-71d8-9616-11dd9011c77a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fbc2-717c-bbc9-c21f6520f960" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fd7b0-fbc2-7c37-98d9-96755dfc6a89" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fbc2-717c-bbc9-c21f6520f960" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-717c-bbc9-c21f6520f960_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fbc2-717c-bbc9-c21f6520f960" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-717c-bbc9-c21f6520f960_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-724c-a201-96df8bdf1cec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fbc2-717c-bbc9-c21f6520f960" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-724c-a201-96df8bdf1cec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019fd7b0-fbc2-763e-886b-5a76c603330d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-724c-a201-96df8bdf1cec" xlink:to="loc_us-gaap_CommonClassAMember_019fd7b0-fbc2-763e-886b-5a76c603330d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019fd7b0-fbc2-7ab1-802f-aa8d85ad26cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fd7b0-fbc2-7c37-98d9-96755dfc6a89" xlink:to="loc_us-gaap_AwardTypeAxis_019fd7b0-fbc2-7ab1-802f-aa8d85ad26cf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fd7b0-fbc2-7ab1-802f-aa8d85ad26cf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019fd7b0-fbc2-7ab1-802f-aa8d85ad26cf" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fd7b0-fbc2-7ab1-802f-aa8d85ad26cf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fd7b0-fbc2-76cd-b77f-97c0c74dcbac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019fd7b0-fbc2-7ab1-802f-aa8d85ad26cf" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fd7b0-fbc2-76cd-b77f-97c0c74dcbac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019fd7b0-fbc2-7c10-aa2d-9699b787fa39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fd7b0-fbc2-76cd-b77f-97c0c74dcbac" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019fd7b0-fbc2-7c10-aa2d-9699b787fa39" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019fd7b0-fbc2-7363-a6a6-09bdd3e5bf64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fd7b0-fbc2-76cd-b77f-97c0c74dcbac" xlink:to="loc_us-gaap_PerformanceSharesMember_019fd7b0-fbc2-7363-a6a6-09bdd3e5bf64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fd7b0-fbc2-7155-b8d9-ca99646743c1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fd7b0-fbc2-7c37-98d9-96755dfc6a89" xlink:to="loc_srt_RangeAxis_019fd7b0-fbc2-7155-b8d9-ca99646743c1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd7b0-fbc2-7155-b8d9-ca99646743c1_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019fd7b0-fbc2-7155-b8d9-ca99646743c1" xlink:to="loc_srt_RangeMember_019fd7b0-fbc2-7155-b8d9-ca99646743c1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd7b0-fbc2-7698-815a-dcde08dd699d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019fd7b0-fbc2-7155-b8d9-ca99646743c1" xlink:to="loc_srt_RangeMember_019fd7b0-fbc2-7698-815a-dcde08dd699d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019fd7b0-fbc2-713c-afff-ba9eed8f0dc1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd7b0-fbc2-7698-815a-dcde08dd699d" xlink:to="loc_srt_MinimumMember_019fd7b0-fbc2-713c-afff-ba9eed8f0dc1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a15ce0-1239-7a77-858d-8abc11b8ac07" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd7b0-fbc2-7698-815a-dcde08dd699d" xlink:to="loc_srt_MaximumMember_01a15ce0-1239-7a77-858d-8abc11b8ac07" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_019fd7b0-fbc2-7a33-990b-601104dc9c19" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fd7b0-fbc2-7c37-98d9-96755dfc6a89" xlink:to="loc_us-gaap_VestingAxis_019fd7b0-fbc2-7a33-990b-601104dc9c19" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019fd7b0-fbc2-7a33-990b-601104dc9c19_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_019fd7b0-fbc2-7a33-990b-601104dc9c19" xlink:to="loc_us-gaap_VestingDomain_019fd7b0-fbc2-7a33-990b-601104dc9c19_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019fd7b0-fbc2-7105-8f8b-f194414c7e9e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_019fd7b0-fbc2-7a33-990b-601104dc9c19" xlink:to="loc_us-gaap_VestingDomain_019fd7b0-fbc2-7105-8f8b-f194414c7e9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_019fd7b0-fbc2-7949-a7b0-81cf4ce62624" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019fd7b0-fbc2-7105-8f8b-f194414c7e9e" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_019fd7b0-fbc2-7949-a7b0-81cf4ce62624" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_019fd7b0-fbc2-7457-941c-bf885d270e5d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019fd7b0-fbc2-7105-8f8b-f194414c7e9e" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_019fd7b0-fbc2-7457-941c-bf885d270e5d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_019fd7b0-fbc2-7f72-b748-d1dbd03a1add" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationAwardTrancheThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019fd7b0-fbc2-7105-8f8b-f194414c7e9e" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_019fd7b0-fbc2-7f72-b748-d1dbd03a1add" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusAxis_019fd7b0-fbc2-708c-bc33-cd0d7a5f5c87" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GranteeStatusAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fd7b0-fbc2-7c37-98d9-96755dfc6a89" xlink:to="loc_us-gaap_GranteeStatusAxis_019fd7b0-fbc2-708c-bc33-cd0d7a5f5c87" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_019fd7b0-fbc2-708c-bc33-cd0d7a5f5c87_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GranteeStatusAxis_019fd7b0-fbc2-708c-bc33-cd0d7a5f5c87" xlink:to="loc_us-gaap_GranteeStatusDomain_019fd7b0-fbc2-708c-bc33-cd0d7a5f5c87_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_019fd7b0-fbc2-7e81-ae9c-41b58d87f6f0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GranteeStatusAxis_019fd7b0-fbc2-708c-bc33-cd0d7a5f5c87" xlink:to="loc_us-gaap_GranteeStatusDomain_019fd7b0-fbc2-7e81-ae9c-41b58d87f6f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_019fd7b0-fbc2-7d80-96be-b12ecaac3bf6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedPaymentArrangementNonemployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_019fd7b0-fbc2-7e81-ae9c-41b58d87f6f0" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_019fd7b0-fbc2-7d80-96be-b12ecaac3bf6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019fd7b0-fbc2-7a15-8f35-00394e0f94ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fd7b0-fbc2-76e0-b574-8a826d449d5f" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019fd7b0-fbc2-7a15-8f35-00394e0f94ab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_CommonStockOutstandingOwnershipPercentage_019fd7b0-fbc2-7af3-9d28-232bab8a2474" xlink:href="mir-20260930.xsd#mir_CommonStockOutstandingOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fd7b0-fbc2-76e0-b574-8a826d449d5f" xlink:to="loc_mir_CommonStockOutstandingOwnershipPercentage_019fd7b0-fbc2-7af3-9d28-232bab8a2474" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019fd7b0-fbc2-7c53-a067-c25aea78cd09" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fd7b0-fbc2-76e0-b574-8a826d449d5f" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019fd7b0-fbc2-7c53-a067-c25aea78cd09" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019fd7b0-fbc2-7c2e-a045-bd37c0c067a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fd7b0-fbc2-76e0-b574-8a826d449d5f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019fd7b0-fbc2-7c2e-a045-bd37c0c067a1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_01a15ce0-1239-703a-a0fb-9c05027000e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fd7b0-fbc2-76e0-b574-8a826d449d5f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_01a15ce0-1239-703a-a0fb-9c05027000e8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019fd7b0-fbc2-7115-be72-3e98db786bcb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fd7b0-fbc2-76e0-b574-8a826d449d5f" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019fd7b0-fbc2-7115-be72-3e98db786bcb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_01a0331b-2150-70d2-8965-89248061277b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fd7b0-fbc2-76e0-b574-8a826d449d5f" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_01a0331b-2150-70d2-8965-89248061277b" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/SegmentInformationScheduleofSegmentReportingInformationbySegmentDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#SegmentInformationScheduleofSegmentReportingInformationbySegmentDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/SegmentInformationScheduleofSegmentReportingInformationbySegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019fd7b0-fbc2-7d8c-91d0-5affecb721c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fd7b0-fbc2-73d6-a6f4-b6661e0578a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fd7b0-fbc2-7d8c-91d0-5affecb721c3" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fd7b0-fbc2-73d6-a6f4-b6661e0578a3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-7672-bfed-4b61befb2f81" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fd7b0-fbc2-73d6-a6f4-b6661e0578a3" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-7672-bfed-4b61befb2f81" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-7672-bfed-4b61befb2f81_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-7672-bfed-4b61befb2f81" xlink:to="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-7672-bfed-4b61befb2f81_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-7a96-8914-c2d3f02d8b80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-7672-bfed-4b61befb2f81" xlink:to="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-7a96-8914-c2d3f02d8b80" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_NuclearSafetySegmentMember_019fd7b0-fbc2-7613-a1ff-9974a6839c98" xlink:href="mir-20260930.xsd#mir_NuclearSafetySegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-7a96-8914-c2d3f02d8b80" xlink:to="loc_mir_NuclearSafetySegmentMember_019fd7b0-fbc2-7613-a1ff-9974a6839c98" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_MedicalSegmentMember_019fd7b0-fbc2-74ab-a030-61e29e6ce3b6" xlink:href="mir-20260930.xsd#mir_MedicalSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-7a96-8914-c2d3f02d8b80" xlink:to="loc_mir_MedicalSegmentMember_019fd7b0-fbc2-74ab-a030-61e29e6ce3b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019fd7b0-fbc2-7ae8-abb6-16a8a9eac2a1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fd7b0-fbc2-73d6-a6f4-b6661e0578a3" xlink:to="loc_srt_ConsolidationItemsAxis_019fd7b0-fbc2-7ae8-abb6-16a8a9eac2a1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019fd7b0-fbc2-7ae8-abb6-16a8a9eac2a1_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019fd7b0-fbc2-7ae8-abb6-16a8a9eac2a1" xlink:to="loc_srt_ConsolidationItemsDomain_019fd7b0-fbc2-7ae8-abb6-16a8a9eac2a1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019fd7b0-fbc2-7c28-a6f8-1e91f9e191db" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019fd7b0-fbc2-7ae8-abb6-16a8a9eac2a1" xlink:to="loc_srt_ConsolidationItemsDomain_019fd7b0-fbc2-7c28-a6f8-1e91f9e191db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019fd7b0-fbc2-7979-a1b2-953ea50769ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019fd7b0-fbc2-7c28-a6f8-1e91f9e191db" xlink:to="loc_us-gaap_OperatingSegmentsMember_019fd7b0-fbc2-7979-a1b2-953ea50769ea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fd7b0-fbc2-7166-9102-ad8fde23adb7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fd7b0-fbc2-73d6-a6f4-b6661e0578a3" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fd7b0-fbc2-7166-9102-ad8fde23adb7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019fd7b0-fbc2-7166-9102-ad8fde23adb7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fd7b0-fbc2-7166-9102-ad8fde23adb7" xlink:to="loc_us-gaap_RelatedPartyDomain_019fd7b0-fbc2-7166-9102-ad8fde23adb7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019fd7b0-fbc2-72d1-a5d5-effbc573c3be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fd7b0-fbc2-7166-9102-ad8fde23adb7" xlink:to="loc_us-gaap_RelatedPartyDomain_019fd7b0-fbc2-72d1-a5d5-effbc573c3be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrelatedPartyMember_019fd7b0-fbc2-73bf-9e6a-addeafd532d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonrelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019fd7b0-fbc2-72d1-a5d5-effbc573c3be" xlink:to="loc_us-gaap_NonrelatedPartyMember_019fd7b0-fbc2-73bf-9e6a-addeafd532d9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019fd7b0-fbc2-72fe-b60f-d65acde79136" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fd7b0-fbc2-7d8c-91d0-5affecb721c3" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019fd7b0-fbc2-72fe-b60f-d65acde79136" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019fd7b0-fbc2-751e-b818-7482a9e0ef00" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fd7b0-fbc2-7d8c-91d0-5affecb721c3" xlink:to="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019fd7b0-fbc2-751e-b818-7482a9e0ef00" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_AdjustedIncomeLossFromOperations_019fd7b0-fbc2-7ec2-aaa8-e9ea7010ea76" xlink:href="mir-20260930.xsd#mir_AdjustedIncomeLossFromOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019fd7b0-fbc2-751e-b818-7482a9e0ef00" xlink:to="loc_mir_AdjustedIncomeLossFromOperations_019fd7b0-fbc2-7ec2-aaa8-e9ea7010ea76" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_019fd7b0-fbc2-7417-b967-212fd1e16009" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019fd7b0-fbc2-751e-b818-7482a9e0ef00" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_019fd7b0-fbc2-7417-b967-212fd1e16009" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_SegmentIncomeFromOperations_019fd7b0-fbc2-766c-91b6-fb25ac971324" xlink:href="mir-20260930.xsd#mir_SegmentIncomeFromOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019fd7b0-fbc2-751e-b818-7482a9e0ef00" xlink:to="loc_mir_SegmentIncomeFromOperations_019fd7b0-fbc2-766c-91b6-fb25ac971324" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_OtherIncomeLoss_019fd7b0-fbc2-7b6e-b8ae-a3d563d04b62" xlink:href="mir-20260930.xsd#mir_OtherIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019fd7b0-fbc2-751e-b818-7482a9e0ef00" xlink:to="loc_mir_OtherIncomeLoss_019fd7b0-fbc2-7b6e-b8ae-a3d563d04b62" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019fd7b0-fbc2-7b06-b545-d9d69cab5ba8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_019fd7b0-fbc2-751e-b818-7482a9e0ef00" xlink:to="loc_us-gaap_OperatingIncomeLoss_019fd7b0-fbc2-7b06-b545-d9d69cab5ba8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIncomeAndExpensesAbstract_019fd7b0-fbc2-7599-b8e9-e7babcf74d46" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherIncomeAndExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fd7b0-fbc2-7d8c-91d0-5affecb721c3" xlink:to="loc_us-gaap_OtherIncomeAndExpensesAbstract_019fd7b0-fbc2-7599-b8e9-e7babcf74d46" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_019fd7b0-fbc2-7fb2-b1ef-7fed751840ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIncomeAndExpensesAbstract_019fd7b0-fbc2-7599-b8e9-e7babcf74d46" xlink:to="loc_us-gaap_InterestExpenseNonoperating_019fd7b0-fbc2-7fb2-b1ef-7fed751840ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInterest_019fd7b0-fbc2-73d6-9a5d-7c767efc84df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIncomeAndExpensesAbstract_019fd7b0-fbc2-7599-b8e9-e7babcf74d46" xlink:to="loc_us-gaap_InvestmentIncomeInterest_019fd7b0-fbc2-73d6-9a5d-7c767efc84df" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019fd7b0-fbc2-72e8-862d-8fd1f7599e9c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIncomeAndExpensesAbstract_019fd7b0-fbc2-7599-b8e9-e7babcf74d46" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019fd7b0-fbc2-72e8-862d-8fd1f7599e9c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyTransactionGainLossBeforeTax_019fd7b0-fbc2-78ef-8daa-522e3b8a66f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignCurrencyTransactionGainLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIncomeAndExpensesAbstract_019fd7b0-fbc2-7599-b8e9-e7babcf74d46" xlink:to="loc_us-gaap_ForeignCurrencyTransactionGainLossBeforeTax_019fd7b0-fbc2-78ef-8daa-522e3b8a66f8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019fd7b0-fbc2-7945-99fc-0845524b746b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIncomeAndExpensesAbstract_019fd7b0-fbc2-7599-b8e9-e7babcf74d46" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019fd7b0-fbc2-7945-99fc-0845524b746b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019fd7b0-fbc2-79e8-abf6-5287faa08f83" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fd7b0-fbc2-7d8c-91d0-5affecb721c3" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019fd7b0-fbc2-79e8-abf6-5287faa08f83" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/SegmentInformationScheduleofCapitalExpendituresandDepreciationandAmortizationDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#SegmentInformationScheduleofCapitalExpendituresandDepreciationandAmortizationDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/SegmentInformationScheduleofCapitalExpendituresandDepreciationandAmortizationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019fd7b0-fbc2-7352-9ba2-67808eee9637" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fd7b0-fbc2-7e35-b1e7-7480f5748551" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fd7b0-fbc2-7352-9ba2-67808eee9637" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fd7b0-fbc2-7e35-b1e7-7480f5748551" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019fd7b0-fbc2-7812-81a1-f25b9c10d644" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fd7b0-fbc2-7e35-b1e7-7480f5748551" xlink:to="loc_srt_ConsolidationItemsAxis_019fd7b0-fbc2-7812-81a1-f25b9c10d644" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019fd7b0-fbc2-7812-81a1-f25b9c10d644_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019fd7b0-fbc2-7812-81a1-f25b9c10d644" xlink:to="loc_srt_ConsolidationItemsDomain_019fd7b0-fbc2-7812-81a1-f25b9c10d644_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019fd7b0-fbc2-7c67-8130-9c61c80f11c0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019fd7b0-fbc2-7812-81a1-f25b9c10d644" xlink:to="loc_srt_ConsolidationItemsDomain_019fd7b0-fbc2-7c67-8130-9c61c80f11c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019fd7b0-fbc2-71ec-86d0-02668ced4d67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019fd7b0-fbc2-7c67-8130-9c61c80f11c0" xlink:to="loc_us-gaap_OperatingSegmentsMember_019fd7b0-fbc2-71ec-86d0-02668ced4d67" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_019fd7b0-fbc2-7b3e-90a1-009df0d884f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019fd7b0-fbc2-7c67-8130-9c61c80f11c0" xlink:to="loc_us-gaap_CorporateNonSegmentMember_019fd7b0-fbc2-7b3e-90a1-009df0d884f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-75d2-9864-e7683fe0a9b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fd7b0-fbc2-7e35-b1e7-7480f5748551" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-75d2-9864-e7683fe0a9b4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-75d2-9864-e7683fe0a9b4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-75d2-9864-e7683fe0a9b4" xlink:to="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-75d2-9864-e7683fe0a9b4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-70b4-8762-456140746556" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-75d2-9864-e7683fe0a9b4" xlink:to="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-70b4-8762-456140746556" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_NuclearSafetySegmentMember_019fd7b0-fbc2-709b-8a1c-6d96d628e8ad" xlink:href="mir-20260930.xsd#mir_NuclearSafetySegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-70b4-8762-456140746556" xlink:to="loc_mir_NuclearSafetySegmentMember_019fd7b0-fbc2-709b-8a1c-6d96d628e8ad" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_MedicalSegmentMember_019fd7b0-fbc2-77f6-888f-228a18363f4e" xlink:href="mir-20260930.xsd#mir_MedicalSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-70b4-8762-456140746556" xlink:to="loc_mir_MedicalSegmentMember_019fd7b0-fbc2-77f6-888f-228a18363f4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_019fd7b0-fbc2-7151-a8bc-9654125a4fdc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CapitalExpendituresIncurredButNotYetPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fd7b0-fbc2-7352-9ba2-67808eee9637" xlink:to="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_019fd7b0-fbc2-7151-a8bc-9654125a4fdc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019fd7b0-fbc2-7888-877d-d8d40346a717" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fd7b0-fbc2-7352-9ba2-67808eee9637" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019fd7b0-fbc2-7888-877d-d8d40346a717" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/SegmentInformationScheduleofRevenuefromExternalCustomersbyGeographicAreasDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#SegmentInformationScheduleofRevenuefromExternalCustomersbyGeographicAreasDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/SegmentInformationScheduleofRevenuefromExternalCustomersbyGeographicAreasDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_019fd7b0-fbc2-771f-888c-bc74aba55e2f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_019fd7b0-fbc2-78db-b334-a2bfb1613883" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_019fd7b0-fbc2-771f-888c-bc74aba55e2f" xlink:to="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_019fd7b0-fbc2-78db-b334-a2bfb1613883" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019fd7b0-fbc2-7cec-8bd2-c4af6a5669f9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_019fd7b0-fbc2-78db-b334-a2bfb1613883" xlink:to="loc_srt_StatementGeographicalAxis_019fd7b0-fbc2-7cec-8bd2-c4af6a5669f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019fd7b0-fbc2-7cec-8bd2-c4af6a5669f9_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019fd7b0-fbc2-7cec-8bd2-c4af6a5669f9" xlink:to="loc_srt_SegmentGeographicalDomain_019fd7b0-fbc2-7cec-8bd2-c4af6a5669f9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019fd7b0-fbc2-7b13-b720-27de31d36cae" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019fd7b0-fbc2-7cec-8bd2-c4af6a5669f9" xlink:to="loc_srt_SegmentGeographicalDomain_019fd7b0-fbc2-7b13-b720-27de31d36cae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NorthAmericaMember_019fd7b0-fbc2-7980-bc81-b0aa9f01c45f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NorthAmericaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fd7b0-fbc2-7b13-b720-27de31d36cae" xlink:to="loc_srt_NorthAmericaMember_019fd7b0-fbc2-7980-bc81-b0aa9f01c45f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EuropeMember_019fd7b0-fbc2-708e-bf23-cfdcdaa2d0d5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EuropeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fd7b0-fbc2-7b13-b720-27de31d36cae" xlink:to="loc_srt_EuropeMember_019fd7b0-fbc2-708e-bf23-cfdcdaa2d0d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AsiaPacificMember_019fd7b0-fbc2-7a31-9626-69cfa55f919d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AsiaPacificMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fd7b0-fbc2-7b13-b720-27de31d36cae" xlink:to="loc_srt_AsiaPacificMember_019fd7b0-fbc2-7a31-9626-69cfa55f919d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-7f0c-ab91-3eb5f02d1891" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_019fd7b0-fbc2-78db-b334-a2bfb1613883" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-7f0c-ab91-3eb5f02d1891" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-7f0c-ab91-3eb5f02d1891_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-7f0c-ab91-3eb5f02d1891" xlink:to="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-7f0c-ab91-3eb5f02d1891_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-79fa-aa04-7c8e3bdfa412" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-7f0c-ab91-3eb5f02d1891" xlink:to="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-79fa-aa04-7c8e3bdfa412" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_NuclearSafetySegmentMember_019fd7b0-fbc2-7e71-9532-8d86c98cd0fe" xlink:href="mir-20260930.xsd#mir_NuclearSafetySegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-79fa-aa04-7c8e3bdfa412" xlink:to="loc_mir_NuclearSafetySegmentMember_019fd7b0-fbc2-7e71-9532-8d86c98cd0fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_MedicalSegmentMember_019fd7b0-fbc2-7ddc-a944-cb5be635886b" xlink:href="mir-20260930.xsd#mir_MedicalSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-79fa-aa04-7c8e3bdfa412" xlink:to="loc_mir_MedicalSegmentMember_019fd7b0-fbc2-7ddc-a944-cb5be635886b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019fd7b0-fbc2-7020-a113-6a59e663cd56" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_019fd7b0-fbc2-771f-888c-bc74aba55e2f" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019fd7b0-fbc2-7020-a113-6a59e663cd56" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/SegmentInformationScheduleofRevenuefromExternalCustomersbyProductsandServicesDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#SegmentInformationScheduleofRevenuefromExternalCustomersbyProductsandServicesDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/SegmentInformationScheduleofRevenuefromExternalCustomersbyProductsandServicesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_019fd7b0-fbc2-7d7e-9cf4-21337000e028" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_019fd7b0-fbc2-70c5-9e59-1bdc32be1d5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_019fd7b0-fbc2-7d7e-9cf4-21337000e028" xlink:to="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_019fd7b0-fbc2-70c5-9e59-1bdc32be1d5b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019fd7b0-fbc2-70e5-9d25-444f2ec34c14" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_019fd7b0-fbc2-70c5-9e59-1bdc32be1d5b" xlink:to="loc_srt_ProductOrServiceAxis_019fd7b0-fbc2-70e5-9d25-444f2ec34c14" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019fd7b0-fbc2-70e5-9d25-444f2ec34c14_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019fd7b0-fbc2-70e5-9d25-444f2ec34c14" xlink:to="loc_srt_ProductsAndServicesDomain_019fd7b0-fbc2-70e5-9d25-444f2ec34c14_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019fd7b0-fbc2-75e3-8755-e2a62d94eb95" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019fd7b0-fbc2-70e5-9d25-444f2ec34c14" xlink:to="loc_srt_ProductsAndServicesDomain_019fd7b0-fbc2-75e3-8755-e2a62d94eb95" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_NuclearPowerMember_019fd7b0-fbc2-75fb-9ac1-79a42f05f38c" xlink:href="mir-20260930.xsd#mir_NuclearPowerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019fd7b0-fbc2-75e3-8755-e2a62d94eb95" xlink:to="loc_mir_NuclearPowerMember_019fd7b0-fbc2-75fb-9ac1-79a42f05f38c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_LabsAndResearchMember_019fd7b0-fbc2-7368-89dd-3cb27fe5a1a3" xlink:href="mir-20260930.xsd#mir_LabsAndResearchMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019fd7b0-fbc2-75e3-8755-e2a62d94eb95" xlink:to="loc_mir_LabsAndResearchMember_019fd7b0-fbc2-7368-89dd-3cb27fe5a1a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_OtherResearchMember_019fd7b0-fbc2-75ef-9f90-bb843ba9192b" xlink:href="mir-20260930.xsd#mir_OtherResearchMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019fd7b0-fbc2-75e3-8755-e2a62d94eb95" xlink:to="loc_mir_OtherResearchMember_019fd7b0-fbc2-75ef-9f90-bb843ba9192b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_CancerCareMember_019fd7b0-fbc2-7ba7-a429-1a02bba4aa5c" xlink:href="mir-20260930.xsd#mir_CancerCareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019fd7b0-fbc2-75e3-8755-e2a62d94eb95" xlink:to="loc_mir_CancerCareMember_019fd7b0-fbc2-7ba7-a429-1a02bba4aa5c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_OtherCareMember_019fd7b0-fbc2-7ec0-8ccf-a969be6bf4dd" xlink:href="mir-20260930.xsd#mir_OtherCareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019fd7b0-fbc2-75e3-8755-e2a62d94eb95" xlink:to="loc_mir_OtherCareMember_019fd7b0-fbc2-7ec0-8ccf-a969be6bf4dd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-76a1-b4a1-7745ca58634a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_019fd7b0-fbc2-70c5-9e59-1bdc32be1d5b" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-76a1-b4a1-7745ca58634a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-76a1-b4a1-7745ca58634a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-76a1-b4a1-7745ca58634a" xlink:to="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-76a1-b4a1-7745ca58634a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-73df-9542-06c340e1b7f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-76a1-b4a1-7745ca58634a" xlink:to="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-73df-9542-06c340e1b7f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_NuclearSafetySegmentMember_019fd7b0-fbc2-7f24-96e1-f544af15a86d" xlink:href="mir-20260930.xsd#mir_NuclearSafetySegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-73df-9542-06c340e1b7f8" xlink:to="loc_mir_NuclearSafetySegmentMember_019fd7b0-fbc2-7f24-96e1-f544af15a86d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_MedicalSegmentMember_019fd7b0-fbc2-78c0-8f51-d5e306db66fb" xlink:href="mir-20260930.xsd#mir_MedicalSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-73df-9542-06c340e1b7f8" xlink:to="loc_mir_MedicalSegmentMember_019fd7b0-fbc2-78c0-8f51-d5e306db66fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019fd7b0-fbc2-73c9-bf21-cdaf7ebfa8d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_019fd7b0-fbc2-7d7e-9cf4-21337000e028" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019fd7b0-fbc2-73c9-bf21-cdaf7ebfa8d9" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/SegmentInformationScheduleofRevenuebyTimingofRecognitionDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#SegmentInformationScheduleofRevenuebyTimingofRecognitionDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/SegmentInformationScheduleofRevenuebyTimingofRecognitionDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EntityWideRevenueMajorCustomerLineItems_019fd7b0-fbc2-76da-8fea-6994ea4f455c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EntityWideRevenueMajorCustomerLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_019fd7b0-fbc2-74ae-ad3c-f40d2390c959" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EntityWideRevenueMajorCustomerLineItems_019fd7b0-fbc2-76da-8fea-6994ea4f455c" xlink:to="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_019fd7b0-fbc2-74ae-ad3c-f40d2390c959" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_019fd7b0-fbc2-7d00-bd56-0444f3db8202" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TimingOfTransferOfGoodOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_019fd7b0-fbc2-74ae-ad3c-f40d2390c959" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_019fd7b0-fbc2-7d00-bd56-0444f3db8202" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_019fd7b0-fbc2-7d00-bd56-0444f3db8202_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_019fd7b0-fbc2-7d00-bd56-0444f3db8202" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_019fd7b0-fbc2-7d00-bd56-0444f3db8202_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_019fd7b0-fbc2-751f-9bbe-74928a7c7857" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_019fd7b0-fbc2-7d00-bd56-0444f3db8202" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_019fd7b0-fbc2-751f-9bbe-74928a7c7857" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferredAtPointInTimeMember_019fd7b0-fbc2-7a82-823a-8a41553463c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransferredAtPointInTimeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_019fd7b0-fbc2-751f-9bbe-74928a7c7857" xlink:to="loc_us-gaap_TransferredAtPointInTimeMember_019fd7b0-fbc2-7a82-823a-8a41553463c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferredOverTimeMember_019fd7b0-fbc2-7c8d-af66-242b57089ced" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransferredOverTimeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_019fd7b0-fbc2-751f-9bbe-74928a7c7857" xlink:to="loc_us-gaap_TransferredOverTimeMember_019fd7b0-fbc2-7c8d-af66-242b57089ced" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019fd7b0-fbc2-7047-bef4-026b595b5c5e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EntityWideRevenueMajorCustomerLineItems_019fd7b0-fbc2-76da-8fea-6994ea4f455c" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019fd7b0-fbc2-7047-bef4-026b595b5c5e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/SegmentInformationScheduleofPropertyPlantandEquipmentbyGeographicalAreasDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#SegmentInformationScheduleofPropertyPlantandEquipmentbyGeographicalAreasDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/SegmentInformationScheduleofPropertyPlantandEquipmentbyGeographicalAreasDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_019fd7b0-fbc2-7015-b3aa-51374c11a305" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_019fd7b0-fbc2-7755-8522-090f2082ae7c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_019fd7b0-fbc2-7015-b3aa-51374c11a305" xlink:to="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_019fd7b0-fbc2-7755-8522-090f2082ae7c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019fd7b0-fbc2-75f4-aefb-5b1b6eee6292" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_019fd7b0-fbc2-7755-8522-090f2082ae7c" xlink:to="loc_srt_StatementGeographicalAxis_019fd7b0-fbc2-75f4-aefb-5b1b6eee6292" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019fd7b0-fbc2-75f4-aefb-5b1b6eee6292_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019fd7b0-fbc2-75f4-aefb-5b1b6eee6292" xlink:to="loc_srt_SegmentGeographicalDomain_019fd7b0-fbc2-75f4-aefb-5b1b6eee6292_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019fd7b0-fbc2-7a19-9c6c-19eac26791a3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019fd7b0-fbc2-75f4-aefb-5b1b6eee6292" xlink:to="loc_srt_SegmentGeographicalDomain_019fd7b0-fbc2-7a19-9c6c-19eac26791a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NorthAmericaMember_019fd7b0-fbc2-7083-8541-06c273f0bd99" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NorthAmericaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fd7b0-fbc2-7a19-9c6c-19eac26791a3" xlink:to="loc_srt_NorthAmericaMember_019fd7b0-fbc2-7083-8541-06c273f0bd99" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EuropeMember_019fd7b0-fbc2-710c-a84a-f7c96c0e87ef" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EuropeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fd7b0-fbc2-7a19-9c6c-19eac26791a3" xlink:to="loc_srt_EuropeMember_019fd7b0-fbc2-710c-a84a-f7c96c0e87ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AsiaPacificMember_019fd7b0-fbc2-759f-9196-7bb79f59c6dc" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AsiaPacificMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fd7b0-fbc2-7a19-9c6c-19eac26791a3" xlink:to="loc_srt_AsiaPacificMember_019fd7b0-fbc2-759f-9196-7bb79f59c6dc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019fd7b0-fbc2-7fe4-899b-7ef344bac0ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_019fd7b0-fbc2-7015-b3aa-51374c11a305" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019fd7b0-fbc2-7fe4-899b-7ef344bac0ed" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/FairValueMeasurementsDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#FairValueMeasurementsDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/FairValueMeasurementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fd7b0-fbc2-7a73-b981-fdf46dea639f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd7b0-fbc2-79db-9ff0-15890b85eb3c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fd7b0-fbc2-7a73-b981-fdf46dea639f" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd7b0-fbc2-79db-9ff0-15890b85eb3c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fd7b0-fbc2-7df3-a07d-1e3d0b87dc29" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd7b0-fbc2-79db-9ff0-15890b85eb3c" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fd7b0-fbc2-7df3-a07d-1e3d0b87dc29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd7b0-fbc2-7df3-a07d-1e3d0b87dc29_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fd7b0-fbc2-7df3-a07d-1e3d0b87dc29" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd7b0-fbc2-7df3-a07d-1e3d0b87dc29_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd7b0-fbc2-71bc-a8e3-265241806def" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fd7b0-fbc2-7df3-a07d-1e3d0b87dc29" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd7b0-fbc2-71bc-a8e3-265241806def" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019fd7b0-fbc2-7d53-8b2d-c47919badb3d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd7b0-fbc2-71bc-a8e3-265241806def" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019fd7b0-fbc2-7d53-8b2d-c47919badb3d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019fd7b0-fbc2-735b-a51f-0878267ce9a7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd7b0-fbc2-71bc-a8e3-265241806def" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019fd7b0-fbc2-735b-a51f-0878267ce9a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019fd7b0-fbc2-7ab8-a1a2-f9e0ba0eeb0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd7b0-fbc2-71bc-a8e3-265241806def" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019fd7b0-fbc2-7ab8-a1a2-f9e0ba0eeb0e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd7b0-fbc2-7fa0-8058-a88067837c05" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd7b0-fbc2-79db-9ff0-15890b85eb3c" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd7b0-fbc2-7fa0-8058-a88067837c05" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-7fa0-8058-a88067837c05_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd7b0-fbc2-7fa0-8058-a88067837c05" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-7fa0-8058-a88067837c05_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-7586-9c3f-fc3ae9f36f66" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd7b0-fbc2-7fa0-8058-a88067837c05" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-7586-9c3f-fc3ae9f36f66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CrossCurrencyInterestRateContractMember_019fd7b0-fbc2-7305-9ac9-a74c4dbd9f9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CrossCurrencyInterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-7586-9c3f-fc3ae9f36f66" xlink:to="loc_us-gaap_CrossCurrencyInterestRateContractMember_019fd7b0-fbc2-7305-9ac9-a74c4dbd9f9d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019fd7b0-fbc2-7605-9958-484b1fb902cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-7586-9c3f-fc3ae9f36f66" xlink:to="loc_us-gaap_InterestRateSwapMember_019fd7b0-fbc2-7605-9958-484b1fb902cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_019fd7b0-fbc2-7a40-8caf-5edac1b154b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fd7b0-fbc2-7a73-b981-fdf46dea639f" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_019fd7b0-fbc2-7a40-8caf-5edac1b154b1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019fd7b0-fbc2-7c00-8206-47ec0221e203" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019fd7b0-fbc2-7a40-8caf-5edac1b154b1" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019fd7b0-fbc2-7c00-8206-47ec0221e203" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_DiscretionaryRetirementPlanAssetsFairValueDisclosure_019fd7b0-fbc2-731a-9d4d-454a901d5fc7" xlink:href="mir-20260930.xsd#mir_DiscretionaryRetirementPlanAssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019fd7b0-fbc2-7a40-8caf-5edac1b154b1" xlink:to="loc_mir_DiscretionaryRetirementPlanAssetsFairValueDisclosure_019fd7b0-fbc2-731a-9d4d-454a901d5fc7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_019fd7b0-fbc2-76ee-96fc-0af39a1a74fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019fd7b0-fbc2-7a40-8caf-5edac1b154b1" xlink:to="loc_us-gaap_DerivativeAssets_019fd7b0-fbc2-76ee-96fc-0af39a1a74fa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019fd7b0-fbc2-7661-8c1b-7bf415409e65" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fd7b0-fbc2-7a73-b981-fdf46dea639f" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019fd7b0-fbc2-7661-8c1b-7bf415409e65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_DiscretionaryRetirementPlanLiabilitiesFairValueDisclosure_019fd7b0-fbc2-7dcc-8c91-f6987e8dc215" xlink:href="mir-20260930.xsd#mir_DiscretionaryRetirementPlanLiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019fd7b0-fbc2-7661-8c1b-7bf415409e65" xlink:to="loc_mir_DiscretionaryRetirementPlanLiabilitiesFairValueDisclosure_019fd7b0-fbc2-7dcc-8c91-f6987e8dc215" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_019fd7b0-fbc2-79d0-a714-30d57e1b6d11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019fd7b0-fbc2-7661-8c1b-7bf415409e65" xlink:to="loc_us-gaap_DerivativeLiabilities_019fd7b0-fbc2-79d0-a714-30d57e1b6d11" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/DerivativesandHedgingNarrativeDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#DerivativesandHedgingNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/DerivativesandHedgingNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-73bf-b144-cc9d4838b1bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_019fd7b0-fbc2-77f5-a4ea-7e81678a498d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-73bf-b144-cc9d4838b1bf" xlink:to="loc_us-gaap_DerivativeTable_019fd7b0-fbc2-77f5-a4ea-7e81678a498d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd7b0-fbc2-7da8-8f74-bbfc7c133402" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019fd7b0-fbc2-77f5-a4ea-7e81678a498d" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd7b0-fbc2-7da8-8f74-bbfc7c133402" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-7da8-8f74-bbfc7c133402_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd7b0-fbc2-7da8-8f74-bbfc7c133402" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-7da8-8f74-bbfc7c133402_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-73b8-ab64-9ad88345f2e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd7b0-fbc2-7da8-8f74-bbfc7c133402" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-73b8-ab64-9ad88345f2e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CrossCurrencyInterestRateContractMember_019fd7b0-fbc2-7437-b218-c80709a08026" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CrossCurrencyInterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-73b8-ab64-9ad88345f2e2" xlink:to="loc_us-gaap_CrossCurrencyInterestRateContractMember_019fd7b0-fbc2-7437-b218-c80709a08026" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019fd7b0-fbc2-7bb6-bded-8b23fd004673" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-73b8-ab64-9ad88345f2e2" xlink:to="loc_us-gaap_InterestRateSwapMember_019fd7b0-fbc2-7bb6-bded-8b23fd004673" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019fd7b0-fbc2-766b-aac9-70c1ac9581b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019fd7b0-fbc2-77f5-a4ea-7e81678a498d" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019fd7b0-fbc2-766b-aac9-70c1ac9581b7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd7b0-fbc2-7689-8792-4bf92c090c57" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019fd7b0-fbc2-77f5-a4ea-7e81678a498d" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd7b0-fbc2-7689-8792-4bf92c090c57" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019fd7b0-fbc2-7689-8792-4bf92c090c57_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd7b0-fbc2-7689-8792-4bf92c090c57" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019fd7b0-fbc2-7689-8792-4bf92c090c57_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019fd7b0-fbc2-7c54-803a-39884c691761" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd7b0-fbc2-7689-8792-4bf92c090c57" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019fd7b0-fbc2-7c54-803a-39884c691761" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019fd7b0-fbc2-75c6-bf69-0a3c6ad4be53" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019fd7b0-fbc2-7c54-803a-39884c691761" xlink:to="loc_us-gaap_CashFlowHedgingMember_019fd7b0-fbc2-75c6-bf69-0a3c6ad4be53" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_DerivativeCrossCurrencyDuration_019fd7b0-fbc2-7925-93c4-207255105ef5" xlink:href="mir-20260930.xsd#mir_DerivativeCrossCurrencyDuration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-73bf-b144-cc9d4838b1bf" xlink:to="loc_mir_DerivativeCrossCurrencyDuration_019fd7b0-fbc2-7925-93c4-207255105ef5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019fd7b0-fbc2-79c0-af8b-a36cff70cab7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-73bf-b144-cc9d4838b1bf" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019fd7b0-fbc2-79c0-af8b-a36cff70cab7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_DerivativeMaximumExposureHedgingDuration_019fd7b0-fbc2-7c17-a7c8-ebe7a540f5f8" xlink:href="mir-20260930.xsd#mir_DerivativeMaximumExposureHedgingDuration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-73bf-b144-cc9d4838b1bf" xlink:to="loc_mir_DerivativeMaximumExposureHedgingDuration_019fd7b0-fbc2-7c17-a7c8-ebe7a540f5f8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax_019fd7b0-fbc2-7b2f-bcfb-d7043a962332" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-73bf-b144-cc9d4838b1bf" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax_019fd7b0-fbc2-7b2f-bcfb-d7043a962332" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax_019fd7b0-fbc2-7a70-af8e-f8f9c562794a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-73bf-b144-cc9d4838b1bf" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax_019fd7b0-fbc2-7a70-af8e-f8f9c562794a" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/DerivativesandHedgingNarrativeDetails_1" xlink:type="simple" xlink:href="mir-20260930.xsd#DerivativesandHedgingNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/DerivativesandHedgingNarrativeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-73bf-b144-cc9d4838b1bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_019fd7b0-fbc2-77f5-a4ea-7e81678a498d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-73bf-b144-cc9d4838b1bf" xlink:to="loc_us-gaap_DerivativeTable_019fd7b0-fbc2-77f5-a4ea-7e81678a498d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd7b0-fbc2-7da8-8f74-bbfc7c133402" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019fd7b0-fbc2-77f5-a4ea-7e81678a498d" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd7b0-fbc2-7da8-8f74-bbfc7c133402" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-7da8-8f74-bbfc7c133402_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd7b0-fbc2-7da8-8f74-bbfc7c133402" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-7da8-8f74-bbfc7c133402_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-73b8-ab64-9ad88345f2e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd7b0-fbc2-7da8-8f74-bbfc7c133402" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-73b8-ab64-9ad88345f2e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CrossCurrencyInterestRateContractMember_019fd7b0-fbc2-7437-b218-c80709a08026" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CrossCurrencyInterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-73b8-ab64-9ad88345f2e2" xlink:to="loc_us-gaap_CrossCurrencyInterestRateContractMember_019fd7b0-fbc2-7437-b218-c80709a08026" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019fd7b0-fbc2-7bb6-bded-8b23fd004673" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-73b8-ab64-9ad88345f2e2" xlink:to="loc_us-gaap_InterestRateSwapMember_019fd7b0-fbc2-7bb6-bded-8b23fd004673" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd7b0-fbc2-7689-8792-4bf92c090c57" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019fd7b0-fbc2-77f5-a4ea-7e81678a498d" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd7b0-fbc2-7689-8792-4bf92c090c57" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019fd7b0-fbc2-7689-8792-4bf92c090c57_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd7b0-fbc2-7689-8792-4bf92c090c57" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019fd7b0-fbc2-7689-8792-4bf92c090c57_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019fd7b0-fbc2-7c54-803a-39884c691761" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd7b0-fbc2-7689-8792-4bf92c090c57" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019fd7b0-fbc2-7c54-803a-39884c691761" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019fd7b0-fbc2-75c6-bf69-0a3c6ad4be53" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019fd7b0-fbc2-7c54-803a-39884c691761" xlink:to="loc_us-gaap_CashFlowHedgingMember_019fd7b0-fbc2-75c6-bf69-0a3c6ad4be53" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_DerivativeCrossCurrencyDuration_019fd7b0-fbc2-7925-93c4-207255105ef5" xlink:href="mir-20260930.xsd#mir_DerivativeCrossCurrencyDuration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-73bf-b144-cc9d4838b1bf" xlink:to="loc_mir_DerivativeCrossCurrencyDuration_019fd7b0-fbc2-7925-93c4-207255105ef5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019fd7b0-fbc2-79c0-af8b-a36cff70cab7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-73bf-b144-cc9d4838b1bf" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019fd7b0-fbc2-79c0-af8b-a36cff70cab7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_DerivativeMaximumExposureHedgingDuration_019fd7b0-fbc2-7c17-a7c8-ebe7a540f5f8" xlink:href="mir-20260930.xsd#mir_DerivativeMaximumExposureHedgingDuration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-73bf-b144-cc9d4838b1bf" xlink:to="loc_mir_DerivativeMaximumExposureHedgingDuration_019fd7b0-fbc2-7c17-a7c8-ebe7a540f5f8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax_019fd7b0-fbc2-7b2f-bcfb-d7043a962332" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-73bf-b144-cc9d4838b1bf" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax_019fd7b0-fbc2-7b2f-bcfb-d7043a962332" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax_019fd7b0-fbc2-7a70-af8e-f8f9c562794a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-73bf-b144-cc9d4838b1bf" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax_019fd7b0-fbc2-7a70-af8e-f8f9c562794a" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/DerivativesandHedgingScheduleofDerivativeInstrumentsinStatementofFinancialPositionFairValueDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#DerivativesandHedgingScheduleofDerivativeInstrumentsinStatementofFinancialPositionFairValueDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/DerivativesandHedgingScheduleofDerivativeInstrumentsinStatementofFinancialPositionFairValueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-793d-989c-24b9471ea631" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_019fd7b0-fbc2-71f7-8174-172dfa34558e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-793d-989c-24b9471ea631" xlink:to="loc_us-gaap_DerivativeTable_019fd7b0-fbc2-71f7-8174-172dfa34558e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019fd7b0-fbc2-741b-a75d-8afe620dcf20" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019fd7b0-fbc2-71f7-8174-172dfa34558e" xlink:to="loc_us-gaap_HedgingDesignationAxis_019fd7b0-fbc2-741b-a75d-8afe620dcf20" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019fd7b0-fbc2-741b-a75d-8afe620dcf20_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019fd7b0-fbc2-741b-a75d-8afe620dcf20" xlink:to="loc_us-gaap_HedgingDesignationDomain_019fd7b0-fbc2-741b-a75d-8afe620dcf20_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019fd7b0-fbc2-7657-910b-eff89fde76c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019fd7b0-fbc2-741b-a75d-8afe620dcf20" xlink:to="loc_us-gaap_HedgingDesignationDomain_019fd7b0-fbc2-7657-910b-eff89fde76c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019fd7b0-fbc2-7769-9f9c-bb7f92672bec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019fd7b0-fbc2-7657-910b-eff89fde76c0" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019fd7b0-fbc2-7769-9f9c-bb7f92672bec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd7b0-fbc2-7460-931e-001d701436be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019fd7b0-fbc2-71f7-8174-172dfa34558e" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd7b0-fbc2-7460-931e-001d701436be" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-7460-931e-001d701436be_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd7b0-fbc2-7460-931e-001d701436be" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-7460-931e-001d701436be_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-7b3b-8e86-20b35935e32a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd7b0-fbc2-7460-931e-001d701436be" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-7b3b-8e86-20b35935e32a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_AccruedInterestReceivableMember_01a17966-eec7-7636-8bdb-d0a18a38b820" xlink:href="mir-20260930.xsd#mir_AccruedInterestReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-7b3b-8e86-20b35935e32a" xlink:to="loc_mir_AccruedInterestReceivableMember_01a17966-eec7-7636-8bdb-d0a18a38b820" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CrossCurrencyInterestRateContractMember_019fd7b0-fbc2-7b4b-a85b-d1dd19aaeff1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CrossCurrencyInterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-7b3b-8e86-20b35935e32a" xlink:to="loc_us-gaap_CrossCurrencyInterestRateContractMember_019fd7b0-fbc2-7b4b-a85b-d1dd19aaeff1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019fd7b0-fbc2-7501-b0fd-85a726922725" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-7b3b-8e86-20b35935e32a" xlink:to="loc_us-gaap_InterestRateSwapMember_019fd7b0-fbc2-7501-b0fd-85a726922725" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetsCurrent_019fd7b0-fbc2-7b93-b4c3-413909a14026" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-793d-989c-24b9471ea631" xlink:to="loc_us-gaap_DerivativeAssetsCurrent_019fd7b0-fbc2-7b93-b4c3-413909a14026" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_019fd7b0-fbc2-7cc0-8bd3-4555d2e2efcc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-793d-989c-24b9471ea631" xlink:to="loc_us-gaap_DerivativeAssets_019fd7b0-fbc2-7cc0-8bd3-4555d2e2efcc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilitiesCurrent_019fd7b0-fbc2-78ca-b4e6-eaa88ab4fb82" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-793d-989c-24b9471ea631" xlink:to="loc_us-gaap_DerivativeLiabilitiesCurrent_019fd7b0-fbc2-78ca-b4e6-eaa88ab4fb82" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilitiesNoncurrent_019fd7b0-fbc2-79c2-8aae-a102b35dc4b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-793d-989c-24b9471ea631" xlink:to="loc_us-gaap_DerivativeLiabilitiesNoncurrent_019fd7b0-fbc2-79c2-8aae-a102b35dc4b3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_019fd7b0-fbc2-71dc-b367-605cb6b097fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-793d-989c-24b9471ea631" xlink:to="loc_us-gaap_DerivativeLiabilities_019fd7b0-fbc2-71dc-b367-605cb6b097fa" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/DerivativesandHedgingScheduleofCashFlowHedgesIncludedinAccumulatedOtherComprehensiveIncomeLossDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#DerivativesandHedgingScheduleofCashFlowHedgesIncludedinAccumulatedOtherComprehensiveIncomeLossDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/DerivativesandHedgingScheduleofCashFlowHedgesIncludedinAccumulatedOtherComprehensiveIncomeLossDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-7df9-9bd9-5010c6776608" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_019fd7b0-fbc2-71c9-b516-e0e42e98ae92" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-7df9-9bd9-5010c6776608" xlink:to="loc_us-gaap_DerivativeTable_019fd7b0-fbc2-71c9-b516-e0e42e98ae92" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd7b0-fbc2-7b21-a520-3d167176a79c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019fd7b0-fbc2-71c9-b516-e0e42e98ae92" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd7b0-fbc2-7b21-a520-3d167176a79c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-7b21-a520-3d167176a79c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd7b0-fbc2-7b21-a520-3d167176a79c" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-7b21-a520-3d167176a79c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-735c-8153-4a709b0d385a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd7b0-fbc2-7b21-a520-3d167176a79c" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-735c-8153-4a709b0d385a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CrossCurrencyInterestRateContractMember_019fd7b0-fbc2-7cfd-984c-365ced9617c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CrossCurrencyInterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd7b0-fbc2-735c-8153-4a709b0d385a" xlink:to="loc_us-gaap_CrossCurrencyInterestRateContractMember_019fd7b0-fbc2-7cfd-984c-365ced9617c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd7b0-fbc2-70f6-90fe-b272c362a7f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019fd7b0-fbc2-71c9-b516-e0e42e98ae92" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd7b0-fbc2-70f6-90fe-b272c362a7f4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019fd7b0-fbc2-70f6-90fe-b272c362a7f4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd7b0-fbc2-70f6-90fe-b272c362a7f4" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019fd7b0-fbc2-70f6-90fe-b272c362a7f4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019fd7b0-fbc2-73b7-ba4c-3df7edccb6b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd7b0-fbc2-70f6-90fe-b272c362a7f4" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019fd7b0-fbc2-73b7-ba4c-3df7edccb6b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentHedgingMember_019fd7b0-fbc2-7383-b043-f6792918e5c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetInvestmentHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019fd7b0-fbc2-73b7-ba4c-3df7edccb6b3" xlink:to="loc_us-gaap_NetInvestmentHedgingMember_019fd7b0-fbc2-7383-b043-f6792918e5c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019fd7b0-fbc2-7e2d-9691-1e61c47db3a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-7df9-9bd9-5010c6776608" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019fd7b0-fbc2-7e2d-9691-1e61c47db3a5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossDerivativeExcludedComponentIncreaseDecreaseBeforeAdjustmentsAndTax_019fd7b0-fbc2-761b-8079-2a504e77f2a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossDerivativeExcludedComponentIncreaseDecreaseBeforeAdjustmentsAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd7b0-fbc2-7df9-9bd9-5010c6776608" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossDerivativeExcludedComponentIncreaseDecreaseBeforeAdjustmentsAndTax_019fd7b0-fbc2-761b-8079-2a504e77f2a6" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/EarningsPerShareNarrativeDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#EarningsPerShareNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/EarningsPerShareNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fd7b0-fbc2-72c7-9198-174423c1696c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fd7b0-fbc2-705e-915a-543cc5ada9a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fd7b0-fbc2-72c7-9198-174423c1696c" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fd7b0-fbc2-705e-915a-543cc5ada9a8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019fd7b0-fbc2-7112-8e88-5f9e27ef6366" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fd7b0-fbc2-705e-915a-543cc5ada9a8" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019fd7b0-fbc2-7112-8e88-5f9e27ef6366" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019fd7b0-fbc2-7112-8e88-5f9e27ef6366_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019fd7b0-fbc2-7112-8e88-5f9e27ef6366" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019fd7b0-fbc2-7112-8e88-5f9e27ef6366_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019fd7b0-fbc2-7577-be99-7a6c4d736023" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019fd7b0-fbc2-7112-8e88-5f9e27ef6366" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019fd7b0-fbc2-7577-be99-7a6c4d736023" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019fd7b0-fbc2-7341-b3c3-2ceb831b6f00" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019fd7b0-fbc2-7577-be99-7a6c4d736023" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019fd7b0-fbc2-7341-b3c3-2ceb831b6f00" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fbc2-73f1-a252-3f68bea8676a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fd7b0-fbc2-705e-915a-543cc5ada9a8" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fbc2-73f1-a252-3f68bea8676a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-73f1-a252-3f68bea8676a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fbc2-73f1-a252-3f68bea8676a" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-73f1-a252-3f68bea8676a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-7860-888b-bbc3662e9965" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fbc2-73f1-a252-3f68bea8676a" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-7860-888b-bbc3662e9965" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019fd7b0-fbc2-797e-95ec-2876dd1fe6c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-7860-888b-bbc3662e9965" xlink:to="loc_us-gaap_CommonClassAMember_019fd7b0-fbc2-797e-95ec-2876dd1fe6c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019fd7b0-fbc2-7f43-8c52-006c209be795" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-7860-888b-bbc3662e9965" xlink:to="loc_us-gaap_CommonClassBMember_019fd7b0-fbc2-7f43-8c52-006c209be795" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-7a25-b7d3-106996176666" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fd7b0-fbc2-705e-915a-543cc5ada9a8" xlink:to="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-7a25-b7d3-106996176666" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-7a25-b7d3-106996176666_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-7a25-b7d3-106996176666" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-7a25-b7d3-106996176666_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-7f97-a04a-f31d7cf7096a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd7b0-fbc2-7a25-b7d3-106996176666" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-7f97-a04a-f31d7cf7096a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ConvertibleSeniorNotesDue2030NotesMember_019fd7b0-fbc2-772f-85ad-e67840bd8ec6" xlink:href="mir-20260930.xsd#mir_ConvertibleSeniorNotesDue2030NotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-7f97-a04a-f31d7cf7096a" xlink:to="loc_mir_ConvertibleSeniorNotesDue2030NotesMember_019fd7b0-fbc2-772f-85ad-e67840bd8ec6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ConvertibleSeniorNotesDue2031NotesMember_019fd7b0-fbc2-705f-a611-ceec01556844" xlink:href="mir-20260930.xsd#mir_ConvertibleSeniorNotesDue2031NotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd7b0-fbc2-7f97-a04a-f31d7cf7096a" xlink:to="loc_mir_ConvertibleSeniorNotesDue2031NotesMember_019fd7b0-fbc2-705f-a611-ceec01556844" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fbc2-79f6-913f-c61c9e175913" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fd7b0-fbc2-705e-915a-543cc5ada9a8" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fbc2-79f6-913f-c61c9e175913" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-79f6-913f-c61c9e175913_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fbc2-79f6-913f-c61c9e175913" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-79f6-913f-c61c9e175913_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-76b5-b353-af62f45b6ef5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd7b0-fbc2-79f6-913f-c61c9e175913" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-76b5-b353-af62f45b6ef5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_019fd7b0-fbc2-7132-90bc-140a8d6ebaf4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd7b0-fbc2-76b5-b353-af62f45b6ef5" xlink:to="loc_us-gaap_ConvertibleDebtMember_019fd7b0-fbc2-7132-90bc-140a8d6ebaf4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019fd7b0-fbc2-7e7b-80ae-114c1f9103f0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fd7b0-fbc2-72c7-9198-174423c1696c" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019fd7b0-fbc2-7e7b-80ae-114c1f9103f0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_CommonStockNumberOfVotesPerCommonShare_019fd7b0-fbc2-78ac-aee5-7d4ab0b23869" xlink:href="mir-20260930.xsd#mir_CommonStockNumberOfVotesPerCommonShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fd7b0-fbc2-72c7-9198-174423c1696c" xlink:to="loc_mir_CommonStockNumberOfVotesPerCommonShare_019fd7b0-fbc2-78ac-aee5-7d4ab0b23869" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_CommonStockConvertibleConversionRatio_019fd7b0-fbc2-7bcf-b1ed-dda696e34c4f" xlink:href="mir-20260930.xsd#mir_CommonStockConvertibleConversionRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fd7b0-fbc2-72c7-9198-174423c1696c" xlink:to="loc_mir_CommonStockConvertibleConversionRatio_019fd7b0-fbc2-7bcf-b1ed-dda696e34c4f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019fd7b0-fbc2-7768-ba35-a38429b515fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fd7b0-fbc2-72c7-9198-174423c1696c" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019fd7b0-fbc2-7768-ba35-a38429b515fb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_019fd7b0-fbc2-7ca4-9488-ccd1394e1d7d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentConvertibleConversionRatio1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fd7b0-fbc2-72c7-9198-174423c1696c" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_019fd7b0-fbc2-7ca4-9488-ccd1394e1d7d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_DebtInstrumentPrincipalAmountForTradingPricePerNote_019fd7b0-fbc2-7cd9-9789-d43113561f28" xlink:href="mir-20260930.xsd#mir_DebtInstrumentPrincipalAmountForTradingPricePerNote"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fd7b0-fbc2-72c7-9198-174423c1696c" xlink:to="loc_mir_DebtInstrumentPrincipalAmountForTradingPricePerNote_019fd7b0-fbc2-7cd9-9789-d43113561f28" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/RestructuringandImpairmentScheduleofRestructuringReservebyTypeofCostDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#RestructuringandImpairmentScheduleofRestructuringReservebyTypeofCostDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/RestructuringandImpairmentScheduleofRestructuringReservebyTypeofCostDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_019fd7b0-fbc2-72b0-a8bf-7c3bc83b4af9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019fd7b0-fbc2-7699-ae20-cebe75f01c74" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019fd7b0-fbc2-72b0-a8bf-7c3bc83b4af9" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019fd7b0-fbc2-7699-ae20-cebe75f01c74" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019fd7b0-fbc2-7339-82e4-49d036b7972c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019fd7b0-fbc2-7699-ae20-cebe75f01c74" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019fd7b0-fbc2-7339-82e4-49d036b7972c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCosts_019fd7b0-fbc2-7e9d-8003-771e786aa558" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019fd7b0-fbc2-72b0-a8bf-7c3bc83b4af9" xlink:to="loc_us-gaap_RestructuringCosts_019fd7b0-fbc2-7e9d-8003-771e786aa558" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostsAndAssetImpairmentCharges_019fd7b0-fbc2-7614-bbf4-02f34e510441" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCostsAndAssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019fd7b0-fbc2-72b0-a8bf-7c3bc83b4af9" xlink:to="loc_us-gaap_RestructuringCostsAndAssetImpairmentCharges_019fd7b0-fbc2-7614-bbf4-02f34e510441" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/RestructuringandImpairmentScheduleofRestructuringReservebyTypeofCostDetails_1" xlink:type="simple" xlink:href="mir-20260930.xsd#RestructuringandImpairmentScheduleofRestructuringReservebyTypeofCostDetails_1"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/RestructuringandImpairmentScheduleofRestructuringReservebyTypeofCostDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_019fd7b0-fbc2-72b0-a8bf-7c3bc83b4af9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019fd7b0-fbc2-7699-ae20-cebe75f01c74" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019fd7b0-fbc2-72b0-a8bf-7c3bc83b4af9" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019fd7b0-fbc2-7699-ae20-cebe75f01c74" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCosts_019fd7b0-fbc2-7e9d-8003-771e786aa558" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019fd7b0-fbc2-72b0-a8bf-7c3bc83b4af9" xlink:to="loc_us-gaap_RestructuringCosts_019fd7b0-fbc2-7e9d-8003-771e786aa558" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostsAndAssetImpairmentCharges_019fd7b0-fbc2-7614-bbf4-02f34e510441" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCostsAndAssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019fd7b0-fbc2-72b0-a8bf-7c3bc83b4af9" xlink:to="loc_us-gaap_RestructuringCostsAndAssetImpairmentCharges_019fd7b0-fbc2-7614-bbf4-02f34e510441" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/RestructuringandImpairmentScheduleofRestructuringExpensesDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#RestructuringandImpairmentScheduleofRestructuringExpensesDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/RestructuringandImpairmentScheduleofRestructuringExpensesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_019fd7b0-fbc2-7012-a362-74249a4d9391" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019fd7b0-fbc2-7e7d-bf85-7a3870df67ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019fd7b0-fbc2-7012-a362-74249a4d9391" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019fd7b0-fbc2-7e7d-bf85-7a3870df67ee" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019fd7b0-fbc2-7b3a-98ea-fd3c7ad15cfa" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019fd7b0-fbc2-7e7d-bf85-7a3870df67ee" xlink:to="loc_srt_ConsolidationItemsAxis_019fd7b0-fbc2-7b3a-98ea-fd3c7ad15cfa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019fd7b0-fbc2-7b3a-98ea-fd3c7ad15cfa_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019fd7b0-fbc2-7b3a-98ea-fd3c7ad15cfa" xlink:to="loc_srt_ConsolidationItemsDomain_019fd7b0-fbc2-7b3a-98ea-fd3c7ad15cfa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019fd7b0-fbc2-746b-91ad-fe5d31e85864" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019fd7b0-fbc2-7b3a-98ea-fd3c7ad15cfa" xlink:to="loc_srt_ConsolidationItemsDomain_019fd7b0-fbc2-746b-91ad-fe5d31e85864" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019fd7b0-fbc2-7706-a5ec-df59745123c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019fd7b0-fbc2-746b-91ad-fe5d31e85864" xlink:to="loc_us-gaap_OperatingSegmentsMember_019fd7b0-fbc2-7706-a5ec-df59745123c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_019fd7b0-fbc2-7f75-ab08-6cc363af739b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019fd7b0-fbc2-746b-91ad-fe5d31e85864" xlink:to="loc_us-gaap_CorporateNonSegmentMember_019fd7b0-fbc2-7f75-ab08-6cc363af739b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-7953-abe0-c4abb3063054" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019fd7b0-fbc2-7e7d-bf85-7a3870df67ee" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-7953-abe0-c4abb3063054" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-7953-abe0-c4abb3063054_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-7953-abe0-c4abb3063054" xlink:to="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-7953-abe0-c4abb3063054_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-7058-b9f0-b6b4c37060e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fd7b0-fbc2-7953-abe0-c4abb3063054" xlink:to="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-7058-b9f0-b6b4c37060e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_NuclearSafetySegmentMember_019fd7b0-fbc2-722f-aa87-06a43f228020" xlink:href="mir-20260930.xsd#mir_NuclearSafetySegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-7058-b9f0-b6b4c37060e5" xlink:to="loc_mir_NuclearSafetySegmentMember_019fd7b0-fbc2-722f-aa87-06a43f228020" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_MedicalSegmentMember_019fd7b0-fbc2-73dc-b65e-1423561c5dbf" xlink:href="mir-20260930.xsd#mir_MedicalSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fd7b0-fbc2-7058-b9f0-b6b4c37060e5" xlink:to="loc_mir_MedicalSegmentMember_019fd7b0-fbc2-73dc-b65e-1423561c5dbf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostsAndAssetImpairmentCharges_019fd7b0-fbc2-79f0-bd5f-f4f9eb94ddec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCostsAndAssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019fd7b0-fbc2-7012-a362-74249a4d9391" xlink:to="loc_us-gaap_RestructuringCostsAndAssetImpairmentCharges_019fd7b0-fbc2-79f0-bd5f-f4f9eb94ddec" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/NoncontrollingInterestsDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#NoncontrollingInterestsDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/NoncontrollingInterestsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestLineItems_019fd7b0-fbc2-7ee2-8221-e912b12cfb5e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MinorityInterestLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestTable_019fd7b0-fbc2-75bb-9ab6-0e7cd9575c32" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MinorityInterestTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MinorityInterestLineItems_019fd7b0-fbc2-7ee2-8221-e912b12cfb5e" xlink:to="loc_us-gaap_MinorityInterestTable_019fd7b0-fbc2-75bb-9ab6-0e7cd9575c32" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fbc2-76b0-b3de-8f061757540c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MinorityInterestTable_019fd7b0-fbc2-75bb-9ab6-0e7cd9575c32" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fbc2-76b0-b3de-8f061757540c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-76b0-b3de-8f061757540c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fbc2-76b0-b3de-8f061757540c" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-76b0-b3de-8f061757540c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-7c62-b532-230baae44092" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd7b0-fbc2-76b0-b3de-8f061757540c" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-7c62-b532-230baae44092" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019fd7b0-fbc2-744d-b41c-fec1309b1b07" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-7c62-b532-230baae44092" xlink:to="loc_us-gaap_CommonClassAMember_019fd7b0-fbc2-744d-b41c-fec1309b1b07" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019fd7b0-fbc2-71ab-ac82-6fb57ac0b393" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-7c62-b532-230baae44092" xlink:to="loc_us-gaap_CommonClassBMember_019fd7b0-fbc2-71ab-ac82-6fb57ac0b393" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_IntermediatecoClassBCommonStockMember_019fd7b0-fbc2-72e1-aed2-a32c4cf068e9" xlink:href="mir-20260930.xsd#mir_IntermediatecoClassBCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-7c62-b532-230baae44092" xlink:to="loc_mir_IntermediatecoClassBCommonStockMember_019fd7b0-fbc2-72e1-aed2-a32c4cf068e9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_IntermediateCoClassBCommonStockMember_019fd7b0-fbc2-76b5-ae82-e9a09047106c" xlink:href="mir-20260930.xsd#mir_IntermediateCoClassBCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd7b0-fbc2-7c62-b532-230baae44092" xlink:to="loc_mir_IntermediateCoClassBCommonStockMember_019fd7b0-fbc2-76b5-ae82-e9a09047106c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fd7b0-fbc2-7441-808f-822e02049bfd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MinorityInterestTable_019fd7b0-fbc2-75bb-9ab6-0e7cd9575c32" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fd7b0-fbc2-7441-808f-822e02049bfd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fbc2-7441-808f-822e02049bfd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd7b0-fbc2-7441-808f-822e02049bfd" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fbc2-7441-808f-822e02049bfd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fbc2-7e3f-b639-f53fe1d58261" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd7b0-fbc2-7441-808f-822e02049bfd" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fbc2-7e3f-b639-f53fe1d58261" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_IntermediateCoMember_019fd7b0-fbc2-7113-b826-188f125a2ce6" xlink:href="mir-20260930.xsd#mir_IntermediateCoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd7b0-fbc2-7e3f-b639-f53fe1d58261" xlink:to="loc_mir_IntermediateCoMember_019fd7b0-fbc2-7113-b826-188f125a2ce6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019fd7b0-fbc2-7442-b0a7-0c5b8b9aaba0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MinorityInterestTable_019fd7b0-fbc2-75bb-9ab6-0e7cd9575c32" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019fd7b0-fbc2-7442-b0a7-0c5b8b9aaba0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fd7b0-fbc2-7442-b0a7-0c5b8b9aaba0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019fd7b0-fbc2-7442-b0a7-0c5b8b9aaba0" xlink:to="loc_us-gaap_EquityComponentDomain_019fd7b0-fbc2-7442-b0a7-0c5b8b9aaba0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fd7b0-fbc2-7659-9fe7-f853465db558" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019fd7b0-fbc2-7442-b0a7-0c5b8b9aaba0" xlink:to="loc_us-gaap_EquityComponentDomain_019fd7b0-fbc2-7659-9fe7-f853465db558" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_019fd7b0-fbc2-75f8-8412-3f2abc7d4dd2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd7b0-fbc2-7659-9fe7-f853465db558" xlink:to="loc_us-gaap_NoncontrollingInterestMember_019fd7b0-fbc2-75f8-8412-3f2abc7d4dd2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_CommonStockConvertibleConversionRatio_019fd7b0-fbc2-7757-99e6-a78266e111ef" xlink:href="mir-20260930.xsd#mir_CommonStockConvertibleConversionRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_019fd7b0-fbc2-7ee2-8221-e912b12cfb5e" xlink:to="loc_mir_CommonStockConvertibleConversionRatio_019fd7b0-fbc2-7757-99e6-a78266e111ef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_ClassOfWarrantOrRightRedemptionThresholdConsecutiveTradingPeriod_019fd7b0-fbc2-733a-b52a-f1e47b3d0295" xlink:href="mir-20260930.xsd#mir_ClassOfWarrantOrRightRedemptionThresholdConsecutiveTradingPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_019fd7b0-fbc2-7ee2-8221-e912b12cfb5e" xlink:to="loc_mir_ClassOfWarrantOrRightRedemptionThresholdConsecutiveTradingPeriod_019fd7b0-fbc2-733a-b52a-f1e47b3d0295" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019fd7b0-fbc2-7d4e-9fc7-8f91d79585cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_019fd7b0-fbc2-7ee2-8221-e912b12cfb5e" xlink:to="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019fd7b0-fbc2-7d4e-9fc7-8f91d79585cd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BusinessAcquisitionPercentageOfNonVotingInterestsNotAttributablePortion_019fd7b0-fbc2-7654-9583-fc4e451afdda" xlink:href="mir-20260930.xsd#mir_BusinessAcquisitionPercentageOfNonVotingInterestsNotAttributablePortion"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_019fd7b0-fbc2-7ee2-8221-e912b12cfb5e" xlink:to="loc_mir_BusinessAcquisitionPercentageOfNonVotingInterestsNotAttributablePortion_019fd7b0-fbc2-7654-9583-fc4e451afdda" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019fd7b0-fbc2-7dd5-bc11-055347267ab8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_019fd7b0-fbc2-7ee2-8221-e912b12cfb5e" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019fd7b0-fbc2-7dd5-bc11-055347267ab8" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mirion.com/role/AccumulatedOtherComprehensiveLossDetails" xlink:type="simple" xlink:href="mir-20260930.xsd#AccumulatedOtherComprehensiveLossDetails"/>
  <link:definitionLink xlink:role="http://www.mirion.com/role/AccumulatedOtherComprehensiveLossDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019fd7b0-fbc2-751f-8e6a-4347ebd37f39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019fd7b0-fbc2-7713-9e43-cc51f36b483a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019fd7b0-fbc2-751f-8e6a-4347ebd37f39" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019fd7b0-fbc2-7713-9e43-cc51f36b483a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019fd7b0-fbc2-7d14-906d-bcbe752cc50e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019fd7b0-fbc2-7713-9e43-cc51f36b483a" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019fd7b0-fbc2-7d14-906d-bcbe752cc50e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fd7b0-fbc2-7d14-906d-bcbe752cc50e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019fd7b0-fbc2-7d14-906d-bcbe752cc50e" xlink:to="loc_us-gaap_EquityComponentDomain_019fd7b0-fbc2-7d14-906d-bcbe752cc50e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fd7b0-fbc2-7e4c-9e7d-252fa305ba06" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019fd7b0-fbc2-7d14-906d-bcbe752cc50e" xlink:to="loc_us-gaap_EquityComponentDomain_019fd7b0-fbc2-7e4c-9e7d-252fa305ba06" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedForeignCurrencyAdjustmentIncludingPortionAttributableToNoncontrollingInterestMember_019fd7b0-fbc2-786d-80f5-f7aa46f82727" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedForeignCurrencyAdjustmentIncludingPortionAttributableToNoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd7b0-fbc2-7e4c-9e7d-252fa305ba06" xlink:to="loc_us-gaap_AccumulatedForeignCurrencyAdjustmentIncludingPortionAttributableToNoncontrollingInterestMember_019fd7b0-fbc2-786d-80f5-f7aa46f82727" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentIncludingPortionAttributableToNoncontrollingInterestMember_019fd7b0-fbc2-7ba3-bdaa-7aa556f10b39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentIncludingPortionAttributableToNoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd7b0-fbc2-7e4c-9e7d-252fa305ba06" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentIncludingPortionAttributableToNoncontrollingInterestMember_019fd7b0-fbc2-7ba3-bdaa-7aa556f10b39" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossDerivativeQualifyingAsHedgeExcludedComponentIncludingPortionAttributableToNoncontrollingInterestMember_019fd7b0-fbc2-7aa6-945a-fa6b6e2f04f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossDerivativeQualifyingAsHedgeExcludedComponentIncludingPortionAttributableToNoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd7b0-fbc2-7e4c-9e7d-252fa305ba06" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossDerivativeQualifyingAsHedgeExcludedComponentIncludingPortionAttributableToNoncontrollingInterestMember_019fd7b0-fbc2-7aa6-945a-fa6b6e2f04f2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossCashFlowHedgeIncludingNoncontrollingInterestMember_019fd7b0-fbc2-776a-877d-e93b36e53aa3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedGainLossCashFlowHedgeIncludingNoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd7b0-fbc2-7e4c-9e7d-252fa305ba06" xlink:to="loc_us-gaap_AccumulatedGainLossCashFlowHedgeIncludingNoncontrollingInterestMember_019fd7b0-fbc2-776a-877d-e93b36e53aa3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AociAttributableToNoncontrollingInterestMember_019fd7b0-fbc2-7263-9502-2daf143bc694" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AociAttributableToNoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd7b0-fbc2-7e4c-9e7d-252fa305ba06" xlink:to="loc_us-gaap_AociAttributableToNoncontrollingInterestMember_019fd7b0-fbc2-7263-9502-2daf143bc694" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fd7b0-fbc2-7917-94a3-9d556cae76df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd7b0-fbc2-7e4c-9e7d-252fa305ba06" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fd7b0-fbc2-7917-94a3-9d556cae76df" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019fd7b0-fbc2-7333-a403-f9e64c08283d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019fd7b0-fbc2-751f-8e6a-4347ebd37f39" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019fd7b0-fbc2-7333-a403-f9e64c08283d" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2026/ecd-2026.xsd#IndividualsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllIndividualsMember" xlink:href="https://xbrl.sec.gov/ecd/2026/ecd-2026.xsd#ecd_AllIndividualsMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_LoicEloyMember_01a13fd9-2038-7451-aed2-90a639f4b70c" xlink:href="mir-20260930.xsd#mir_LoicEloyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_mir_LoicEloyMember_01a13fd9-2038-7451-aed2-90a639f4b70c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_mir_BrianSchopferMember_019fd7b0-f961-75e7-9ed8-ab0e9be18c00" xlink:href="mir-20260930.xsd#mir_BrianSchopferMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_mir_BrianSchopferMember_019fd7b0-f961-75e7-9ed8-ab0e9be18c00" xlink:type="arc" order="3"/>
  </link:definitionLink>
</link:linkbase>
