William X. O’Brien, politician and trade unionist, is born on January 23, 1881, in Clonakilty, County Cork. He is christened “John William.”

O’Brien moves with his family to Dublin in 1897, and quickly becomes involved in the Irish Socialist Republican Party (ISRP). He is described as “a very significant figure in the ISRP” by ISRP historian David Lynch. He is a member of the Socialist Party of Ireland, serving on its executive.

A close friend and associate of James Connolly, O’Brien helps establish the Irish Transport and General Workers’ Union (ITGWU) in 1909 and is instrumental in the Dublin lock-out strike in 1913.

A member of the Irish Neutrality League and Anti-Conscription Committee during World War I, O’Brien is interned on several occasions by the Dublin Castle government. During one of these instances, he stands in the 1920 Stockport by-election, but is refused a release to campaign in it.

With the formation of the Irish Free State, O’Brien is elected as Teachta Dála (TD) for Dublin South at the 1922 general election, and again for Tipperary in June 1927 and again in 1937.

An important figure in the Labour Party in Ireland in its formative days, O’Brien resists James Larkin‘s attempt to gain control of the Party on release from prison. Taking Larkin to court over his occupation of ITGWU headquarters, the Larkin-O’Brien feud results in a split within the labour and trade union movements, and the formation of the Irish Congress of Trade Unions.

In 1930, O’Brien seeks to have Leon Trotsky granted asylum in Ireland, but the head of the Free State government, W. T. Cosgrave, refuses to allow it.

Active in politics and the trade union movement into his 60s, O’Brien retires in 1946 and dies on October 31, 1968.