Existing research frames ethnonationalism as homophobic, in which the queer is positioned outside of the boundaries of the ethnic nation. Less well understood is how LGBTQ activism engages with ethnonationalism, particularly in relation to questions of national self-determination. The limited research on this issue frames LGBTQ activist movements as groups that reject divisive ethnonationalisms by forging alternative cosmopolitan and transnational expressions of sexual identity. By exploring a single case-study, Northern Ireland, this article draws attention to how LGBTQ movements can be sites of conflict over questions of national self-determination, particularly when sexual liberation is wedded to anti-imperialist struggles. The paper concludes by reaffirming Horowitz’s model of ethnic seepage, in which the dominant ethnonational cleavages infuse all issues in divided societies. The article uses a wide range of primary data, including interviews and archival documents, to analyze LGBTQ activism in Northern Ireland during the period of ethnonationalist conflict in the 1970s and 1980s.