He took part in the Easter Rising in 1916. Elected to Parliament as a member of Sinn Fein in 1919, he became Minister of Finance in the self-declared Irish government, at the same time directing the Irish Republican Army’s guerrilla campaign against the British. He was one of the negotiators of the Anglo-Irish Treaty of 1921 and commanded the Irish Free State forces in the civil war that followed partition. On the death of Arthur Griffith in 1922, he became head of the government, but was shot in an ambush ten days later.