Margaret Olwen MacMillan was born in Toronto in 1943. After earning an Honours B.A. in Modern History from the University of Toronto, she completed a B.Phil. in Politics at Oxford University, where she subsequently wrote her doctoral thesis on the social and political attitudes of the British in India.

From 1975 to 2002, Dr. MacMillan was a Professor of History at Ryerson University including five years as departmental chair. In addition to her teaching in the classroom and academic publications, she has collaborated with Professor Robert Bothwell on an innovative series of educational radio programmes for CJRT/Open College on international relations. In 2002, she was named Provost of Trinity College and a Professor of History at the University of Toronto.