Supported by UK and Irish membership of the European Union (EU), the 1998 Belfast/Good Friday Agreement's post-sovereignist compromise helped to diminish the contested politics of the border in Ireland. However, by altering the status of the border, Brexit aroused and fomented politically charged divisions in Northern Ireland. We explore the confluence of four consequences of Brexit for Northern Ireland. Firstly, we detail how Brexit highlights the inadequacies and dysfunction of the UK's territorial architecture. Second, we examine the specific structural, institutional and relational weaknesses of Northern Ireland's devolved system. Third, we explain how Brexit further weakened the scaffolding that supports Northern Ireland's devolved settlement. And fourth, we explore why Brexit has prompted profound reconsideration of the UK's existing territorial set-up. Brexit's challenge to the status quo in Northern Ireland, and by extension the UK's constitutional and territorial integrity, is linked not just to internal political dynamics in Northern Ireland, but also to the ambiguity of the existing asymmetrical UK devolution settlement, its lack of embeddedness within the UK constitutional order and the absence of binding cultural narratives. Finally, we extend this analysis to posit that Brexit has revived the 'Irish question' and stirred a potentially destabilizing debate about Irish unity.