© 2021 Informa UK Limited, trading as Taylor & Francis Group. Having been issues which stimulated little discussion beyond Northern Ireland before the Brexit referendum, the ‘Irish issue’ dominated and complicated the subsequent EU–UK withdrawal negotiations. The ‘taking back control’ narrative bears the hallmarks of Prime Minister Boris Johnson’s notion of a ‘recaptured sovereignty’. This conception of sovereignty, however, clashes with the post-sovereign character and content of the 1998 Belfast/Good Friday Agreement. The institutions created by the Agreement move beyond the old frameworks for political order by creating a series of interlocking territorial, cross-territorial, and cross-national institutions based on shared sovereignty. This prompts critical questions about the resilience and sustainability of the Agreement against the backdrop of a shift in sovereignty which appears incompatible with the key tenets of Northern Ireland’s peace agreement. This article examines how Northern Ireland’s approach to and experience of the EU referendum differed from the rest of the UK. It queries how the referendum result, subsequent political and electoral developments, and difficulties in agreeing a withdrawal formula and future UK–EU relationship, expose the gap between the UK’s commitments to a post-sovereign arrangement for Northern Ireland and the preference for a return to an older conception of sovereignty as implied by the Brexit vote.