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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019e50db-c117-7366-895a-f63ea0c01625,g:e70a5977-fb16-4334-b3ea-f330a3ec00fa-->
<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://riministreet.com/role/Cover" xlink:type="simple" xlink:href="rmni-20260604.xsd#Cover"/>
  <link:definitionLink xlink:role="http://riministreet.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_019e50db-c117-7404-bd2f-a95fe08542e8" 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_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_DocumentInformationTable_019e50db-c117-7404-bd2f-a95fe08542e8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019e50db-c117-7a14-a6d6-427cef478111" 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_dei_DocumentInformationTable_019e50db-c117-7404-bd2f-a95fe08542e8" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019e50db-c117-7a14-a6d6-427cef478111" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e50db-c117-7a14-a6d6-427cef478111_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_019e50db-c117-7a14-a6d6-427cef478111" xlink:to="loc_us-gaap_EquityComponentDomain_019e50db-c117-7a14-a6d6-427cef478111_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e50db-c117-72be-bc74-1833ad79da49" 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_019e50db-c117-7a14-a6d6-427cef478111" xlink:to="loc_us-gaap_EquityComponentDomain_019e50db-c117-72be-bc74-1833ad79da49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019e50db-c117-7923-87ee-6bced5b6da68" 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_019e50db-c117-72be-bc74-1833ad79da49" xlink:to="loc_us-gaap_CommonStockMember_019e50db-c117-7923-87ee-6bced5b6da68" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019e50db-c117-7bf2-859f-8dad85e41769" 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_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_EntityCentralIndexKey_019e50db-c117-7bf2-859f-8dad85e41769" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019e50db-c117-7023-b369-12a38c7ba2f5" 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_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_AmendmentFlag_019e50db-c117-7023-b369-12a38c7ba2f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019e50db-c117-7bfb-9ce8-3963fb29ff3a" 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_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_DocumentType_019e50db-c117-7bfb-9ce8-3963fb29ff3a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019e50db-c117-7adb-9296-650cb910a1db" 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_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_DocumentPeriodEndDate_019e50db-c117-7adb-9296-650cb910a1db" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019e50db-c117-7161-97a0-0097e32ce3fa" 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_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_EntityRegistrantName_019e50db-c117-7161-97a0-0097e32ce3fa" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019e50db-c117-716b-ac04-6de952302046" 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_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019e50db-c117-716b-ac04-6de952302046" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019e50db-c117-794b-8d6e-abd8278bad17" 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_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_EntityFileNumber_019e50db-c117-794b-8d6e-abd8278bad17" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019e50db-c117-7250-9e0c-f677db8b399b" 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_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_EntityTaxIdentificationNumber_019e50db-c117-7250-9e0c-f677db8b399b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019e50db-c117-70ca-9454-a3ead2548356" 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_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_EntityAddressAddressLine1_019e50db-c117-70ca-9454-a3ead2548356" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_019e50db-c117-71ee-bf4b-fc879a0b1659" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_EntityAddressAddressLine2_019e50db-c117-71ee-bf4b-fc879a0b1659" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019e50db-c117-7699-b8d4-404af9d59e01" 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_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_EntityAddressCityOrTown_019e50db-c117-7699-b8d4-404af9d59e01" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019e50db-c117-7d72-a20f-d17b39fcfc67" 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_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_EntityAddressStateOrProvince_019e50db-c117-7d72-a20f-d17b39fcfc67" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019e50db-c117-73c4-9926-7b74e2308864" 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_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_EntityAddressPostalZipCode_019e50db-c117-73c4-9926-7b74e2308864" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019e50db-c117-7cae-bd82-2919bab48e38" 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_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_CityAreaCode_019e50db-c117-7cae-bd82-2919bab48e38" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019e50db-c117-7ac6-94b8-d315e1ea865e" 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_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_LocalPhoneNumber_019e50db-c117-7ac6-94b8-d315e1ea865e" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_019e50db-c117-727b-8379-56dfa723a5cd" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_WrittenCommunications_019e50db-c117-727b-8379-56dfa723a5cd" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_019e50db-c117-7143-8e04-634de41d6b3a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_SolicitingMaterial_019e50db-c117-7143-8e04-634de41d6b3a" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_019e50db-c117-751e-a547-b54c25e1ecf9" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_PreCommencementTenderOffer_019e50db-c117-751e-a547-b54c25e1ecf9" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_019e50db-c117-7b40-b618-1bd7d7c76a6c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_019e50db-c117-7b40-b618-1bd7d7c76a6c" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019e50db-c117-7c7d-8237-b8172e05e728" 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_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_Security12bTitle_019e50db-c117-7c7d-8237-b8172e05e728" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019e50db-c117-7e60-9af2-f4c6ad4338fb" 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_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_TradingSymbol_019e50db-c117-7e60-9af2-f4c6ad4338fb" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019e50db-c117-770c-8a31-15f8b203dca5" 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_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_SecurityExchangeName_019e50db-c117-770c-8a31-15f8b203dca5" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019e50db-c117-7caf-ac2b-47401724abf6" 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_019e50db-c117-7a86-bdec-ef1f19271e79" xlink:to="loc_dei_EntityEmergingGrowthCompany_019e50db-c117-7caf-ac2b-47401724abf6" xlink:type="arc" order="22"/>
  </link:definitionLink>
</link:linkbase>
