Connolly was born in Cowgate, Edinburgh, on 5 June 1868. His Irish Catholic parents were poor, and Connolly worked from the age of eleven; in 1882, he falsified his age to join the army. Stationed in Dublin in 1889, he deserted to avoid foreign service. In 1890, he married Lillie Reynolds, a Protestant domestic servant from Co Wicklow, and returned to Edinburgh.

Politically active in Scotland, Connolly became paid organiser of the Dublin Socialist Club in 1906. He founded and became secretary of the Irish Socialist Republican Party, and in 1898 launched the weekly Workers' Republic, exploiting the 1798 centenary to argue that only in a socialist republic could the ideals of Wolfe Tone be realised. He later worked for the new Socialist Labour Party in Scotland, and helped to found the International Workers of the World (the 'Wobblies') in America.

Connolly returned to Ireland in 1910, joining the Socialist Party of Ireland, successor to the ISRP. He soon published Labour, Nationality and Religion, defending a Catholic's right to be a socialist, and Labour in Irish History, describing the working class as 'the incorruptible inheritors of the fight for freedom in Ireland'. In l911, he became Ulster organiser of the Irish Transport and General Workers' Union. headed by James Larkin, and soon called a dock strike in Belfast. When Larkin was imprisoned in 1913, Connolly forced his release by closing the port of Dublin.

Larkin left for America in 1914, and Connolly became acting secretary of the ITGWU, commandant of the recently formed Irish Citizen Army, and editor of the Irish Worker, which was soon suppressed for its anti-war sentiments. He was persuaded by the Irish Republican Brotherhood to support the 1916 rising, and about 120 ICA members took part. Connolly was commandant-general in Dublin, and led the assault on the General Post Office. His left ankle was smashed by a bullet, and after his court martial he was shot at Kilmainham Jail on 12 May 1916.

Kilmainham Jail museum, Dublin.
Ruth Dudley Edwards, James Connolly (1981).