MacDermot was born in Montreal, the son of Canadian diplomat Terence MacDermot and Elizabeth Savage. He was educated at Upper Canada College and Bishop's University (Sherbrooke, Quebec, Canada). He received a Bachelor of Music from Cape Town University, South Africa and made a study of African music his specialty. He also studied the piano privately with Neil Chotem. It was also during his time at Cape Town where he would meet his future wife, Marlene Bruynzeel. They married in 1956 and had five children.