Maclise was born in Cork, Ireland, the son of Alexander McLish (also known as McLeish, McLish, McClisse or McLise), a tanner or shoemaker, but formerly a Scottish Highlander soldier.
Various influential friends recognised Maclise's genius and promise, and were anxious to furnish him with the means of studying in London; but refusing all financial assistance, he saved the money himself and arrived in the capital on 18 July 1827.