Supple began work as coachbuilder in Ireland, but moved to London to further his career in literature. He wrote on secular subjects for the Reasoner (London), edited by George Holyoake. Holyoake wrote that Supple 'had seen patriotic service in 1848, having been concerned in an insurrection planned in Meath' (Sixty Years of an Agitator's Life (1902) vol. 2). Supple also wrote articles for the magazines the Empire, the Morning Star and the Nation, as well as patriotic ballads. After Supple came to Australia, he studied for the bar, and also wrote for the Melbourne newspapers the Herald, the Age and the Argus.
In 1870, Supple was sentenced to hang for murder when he tried to shoot the editor of the Age, George Paton Smith, because of Smith's anti-Irish stance. Supple, due to his near-sightedness, only wounded Smith but unintentionally killed a bystander. After a second trial Supple was sentenced to 20 years jail following intervention by Holyoake and Lord Kimberley (whose timely telegram to Lord Canterbury, the Governor of Victoria, was successful). Despite his ill health while in prison, Supple continued to write in order to support his two sisters. Eight years later, shortly after the death of his original target, he was released .
A week later Supple left Australia to join his sisters in New Zealand. He supported himself and his sisters by working for the New Zealand Herald. His poems appeared in Irish (Hayes's Ballads of Ireland) and Australian (Sladen's Australian Poets 1888) anthologies and Bentley's Miscellany. Supple also wrote The History of the Invasion of Ireland by the Anglo-Normans which was published in Dublin in 1856.
