 Stewart was born in Chicago in 1939 to Henry Stewart and Evangeline (née Williams) Stewart.His father was born in Scotland and emigrated to the United States at the age of 26, where he became a Presbyterian minister and social worker/organizer in the Chicago neighborhoods.Stewart's mother, Evangeline, worked as a University of Chicago librarian, and this, coupled with the help of a scholarship, allowed Stewart to enter the University of Chicago Laboratory Schools, where he remained into his high school years and where he was student body president.