Sir Samuel Thompson Irwin CBE (3 July 1877 – 21 June 1961), often known as S. T. Irwin, was an Irish rugby player, surgeon and unionist politician. Born in Claudy, County Londonderry, Irwin studied at Foyle College and Queen's College, Belfast. While studying, Irwin played for the Irish national rugby union team in nine Home Nations Championship matches, between 1900 and 1903, and he also played cricket to a high level. Irwin's son also played rugby for Ireland and worked as a surgeon.