During that time, he enlisted in the Canadian Army Dental Corps in 1917, being commissioned as a lieutenant, and assigned to Battalion M. D. No.

The Boston Bruins began play in 1924 and losing eight of their first nine games, often by wide margins, and desperate for goaltending, signed Stewart to a contract.

He played the rest of the schedule for Boston, winning five out of twenty-one games for the weak club, adding two shutouts.

His career goals against average is fifth best in Boston Bruins' history for any goaltender playing 75 games or more.

He graduated from the Royal College of Dental Surgeons in 1919, and practiced dentistry in the offseason thereafter.