Stewart's bright football future became clear when he caught a pass
to win the scholastic final in his junior year at Toronto's
Riverdale Collegiate Institute. He was a standout player at Queen's
University from 1953 to 1957, where he became the first to win the
John Evans Memorial Trophy three times as the club's most valuable
player. Upon his graduation, he was the fourth highest scorer in
Queen's history, breaking many of the marks set by fellow Hall of
Famer Pep Leadley.
When Stewart moved to Ottawa to attend law school in 1958, he was quickly signed to a contract by the Ottawa Rough Riders, with whom he enjoyed 12 glorious seasons as a stalwart offensive player. He championed the Rough Riders to four Grey Cup finals and three victories, in 1960, 1968, and 1969.
One of Stewart's greatest moments came in 1960 when, in a game against the Montreal Alouettes, he established a single game rushing record of 287 yards, a mark which stood until 2003. Another career highlight came in a 1969 Grey Cup game in which he extended two passes from Russ Jackson into remarkable touchdown runs, one of which registered as the fifth longest scoring pass in Grey Cup history.
An Eastern Conference All-Star in both 1960 and 1964, Stewart received the Schenley Award and the Lionel Conacher Award as Canada's most outstanding male athlete in 1960. In both 1960 and 1967, he was awarded the Walker Trophy as the Ottawa Club's MVP, and the Jeff Russel Memorial Trophy as the most outstanding player in the CFL's Eastern Division.
Upon his retirement in 1970, Stewart was only one of three native Canadian players who was not a kicker to score more than 400 points. In honour of his achievements on the field, the Rough Riders retired his #11 sweater and, in 1977, he was inducted into the Canadian Football Hall of Fame.