Born in Dublin, the son of John Mallin, a carpenter. He joined the army as a drummer boy, in his teens and served for approximately 14 years. Part of his service took place in India, where he contracted malaria.
After his discharge, he settled in Dublin to work as as a silk weaver, and campaigned for workers’ rights in the Silk Weavers’ Union of which he was secretary. He was also active in the Working Men’s Temperance Club and joined the Irish Citizen Army in November 1913. Due to his dedication, James Connolly promoted him to chief of staﬀ.
Disciplined and a devout Catholic, Mallin used his army experience to train men in marches, ﬁeld manoeuvres and mock attacks on public buildings. With Connolly at the GPO for the Rising, Mallin and his second in command, Countess Markievicz, took charge of the ICA garrison sent to St Stephen’s Green which they fled under fire from British guns for the College of Surgeons.
After the surrender, Mallin was tried by court-martial and sentenced to death. He was survived by his wife Agnes Hickey, his three sons, including Father Joseph Mallin, and two daughters, the younger of whom was not born until four months after his death. Before his death Mallin said: “I am satisfied I have done my duty to my beloved Ireland.” He was executed at Kilmainham on May 8, 1916.