He studied Celtic Studies at University College Dublin, where he was a member of the Irish Republican Army (IRA) training corps. He left before graduating to join the IRA's East Limerick Brigade in 1922. He fought on the Anti-Treaty side in the Irish Civil War, and was wounded and interned. In November 1923 he was released and returned to University College Dublin. He was active in a number of Irish-language societies, winning the Cumann Gaedhealach's gold medal for oratory in Irish in 1924. During the Gaelic Revival era he was commissioned to write for Irish-language publications – he briefly edited "An Reult" (). He formed the University Republican Club and led it on demonstrations before graduation in 1925.