The Good Friday/Belfast Agreement had to address a fissure in constitutional thought on the island of Ireland; was the legitimacy of the island’s constitutional arrangements dependent upon one group of constituent power holders, or two? The question had been contested since partition, and this contribution explores how the conundrum was tackled through John Hume’s concept of a people of Northern Ireland, who would have the ability to determine whether to remain within the UK or join a unified Ireland. This concept might have sufficed during the 1998 negotiations, but it remained all-but-unexplored in the years after, until the aftermath of the June 2016 Brexit referendum. Brexit changed the debate on the (re)unification of Ireland, and this contribution examines three facets of this shift. First, it necessitates a new understanding of this group of constituent power holders. Second, to reflect the 1998 Agreement, the people of Northern Ireland also gained special protections in the UK-EU Withdrawal Agreement. Third, alongside these developments, the UK Government’s application of immigration rules and ascription of nationality to the people of Northern Ireland called the nature of this status into question. This article considers how these factors are shaping contemporary debate over Northern Ireland’s constitutional future.