 Born in Toronto, Ontario, Souster grew up in West Toronto near the Humber River.He joined the Canadian Imperial Bank of Commerce at King & Bay Streets in Toronto in 1939 and, apart from four years' service in the Royal Canadian Air Force during World War II, he worked at the bank until retiring in 1984.Souster's first published poem appeared in "First Statement", the little magazine founded by John Sutherland in Montreal in 1942.