The early history of the Gaelic Athletic Association (GAA) has been described by Richard Holt as ‘certainly the outstanding example of the appropriation of sport by nationalism’ in a British imperial context.1 This statement is most apt to define the association's part in the radicalisation of Ireland in the decade leading up to the independence of most of the island in 1922. In Ulster, the GAA became increasingly embroiled in the political issues of the day, as the spectre of the partition of the northern province came into view and became a reality from 1920. The rapid transformation of the sporting and political landscape was embodied by the career of Owen O'Duffy, whose star rose through the ranks of the GAA in Ulster from 1912 and the revolutionary movement from 1917. This article will explore the nature and extent of change through which the northern province of the GAA passed in the years 1912–1923, and will demonstrate that the personal role of O'Duffy in this process was profound but very opportunistic. Whereas the interlocking of GAA leadership and republican activity propelled O'Duffy to high office in the new Irish Free State regime for the next decade, it produced a much less favourable legacy for GAA members to the north of the Irish border living under an arch-Unionist regime.