Plummer was born in Toronto, Ontario, Canada, the son of Isabella Mary (nÃ?Â©e Abbott) and John Plummer, who was secretary to the Dean of Sciences at McGill University. His maternal great-grandfather was former Canadian Prime Minister Sir John Abbott. Married in February 1929, Plummer's parents were divorced shortly after he was born and he was raised an only child at the Abbott family home at Senneville, Quebec outside Montreal. He studied to be a concert pianist but developed a love for the theatre at an early age and began acting in high school. He travelled by train to gain experience with the Canadian Repertory Theatre (the CRT) in Ottawa.