Short was born in Hamilton, Ontario, the youngest of five children of Olive Grace (née Hayter; 1913–1968), a concertmistress of the Hamilton Symphony Orchestra, and Charles Patrick Short (1909–1970), a corporate executive with Stelco, a Canadian steel company. He and his siblings were raised as Catholics. He had three older brothers, David (now deceased), Michael, and Brian, and one older sister, Nora. Short's father was an Irish Catholic emigrant from Crossmaglen, South Armagh, who came to North America as a stowaway during the Irish War of Independence. Short's mother was of English and Irish descent. She encouraged his early creative endeavours. His eldest brother, David, was killed in a car accident in Montréal, Québec in 1962 when Short was 12. His mother died of cancer in 1968, his father two years later of complications from a stroke.