He was appointed ITGWU National Organiser in 1937, elected Vice President in 1939 and General President in 1946, a position he held until his retirement in 1953. In this position he saw union membership grow from 39717 to 79957 in 1953. This growth reflected McMullan’s attention to organisation, administrative efficiency and industrial militancy.  

When McMullan retired, the ITGWU observed that ‘the movement he served for forty years was transformed from one that was misunderstood and whose objects were maligned to one that had won universal respect with a special place in the councils of the nation.

McMullan was a brilliant, analytic speaker readily filling the void since 1946, not simply because he was the only Ulsterman to become an ITGWU General Officer.  McMullan is a significant figure in ITGWU history.

William McMullan was a trade unionist and politician.Born in Belfast, William began working in the shipyards and became an active trade unionist. He met James Connolly in 1910 and was thereafter Connolly’s most prominent supporter in Belfast, acting as the first chairman of the Irish Labour Party.  In 1912 he moved to Dublin and helped form the Independent Labour Party branch. On his return to Belfast in 1920 he became the Belfast Branch Secretary of the ITGWU. He was elected as a Northern Ireland Labour Party Poor LAW Guardian for Smithfield Ward in 1924, a City Councillor in January 1925 and in June, Stormont MP for West Belfast. In Parliament, William challenged the Ulster Unionist Party over unemployment and in 1928 joined with other NILP members in walking out, earning suspension. He opposed the Boundary Settlement and argued for national unity, a position he held all his life.