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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019c23e7-753e-7733-a607-60d687c79e32,g:f969954e-56e3-4c48-bbcf-f8be5f640855-->
<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" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/PvpDisclosure" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#PvpDisclosure"/>
  <link:presentationLink xlink:role="http://xbrl.sec.gov/ecd/role/PvpDisclosure" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllIndividualsMember" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#ecd_AllIndividualsMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_mgnx_CurrentPEOMember" xlink:href="mgnx-20260407.xsd#mgnx_CurrentPEOMember"/>
    <link:presentationArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_mgnx_CurrentPEOMember" xlink:type="arc" preferredLabel="http://www.xbrl.org/2003/role/label"/>
    <link:loc xlink:type="locator" xlink:label="loc_mgnx_FormerPEOMember" xlink:href="mgnx-20260407.xsd#mgnx_FormerPEOMember"/>
    <link:presentationArc order="2" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_mgnx_FormerPEOMember" xlink:type="arc" preferredLabel="http://www.xbrl.org/2003/role/label"/>
  </link:presentationLink>
</link:linkbase>
