After the war, Stewart was signed by the Chicago White Sox in December 1918,[2][3] but he suffered an arm injury falling down a flight of stairs while working as a census taker,[4] and was sent to the minor leagues in May 1919.

[9] In 1928, Stewart became the NHL's first U.S.-born referee, and served in that capacity until 1941, excepting his two seasons as coach of the Chicago Black Hawks; 1937–38 (when the team won the Stanley Cup) and 1938–39.

[8] Stewart was an umpire in the National League (NL) from 1933 to 1954, and officiated in four World Series (1937, 1943, 1948, 1953) and four All-Star Games (1936, 1940, 1948, 1954), calling balls and strikes for the last contest.

He also was the home plate umpire for Johnny Vander Meer's second consecutive no-hitter in 1938, and was the crew chief for the 1951 three-game pennant playoff between the New York Giants and the Brooklyn Dodgers.

[15] In February 1964, Stewart died at the Veterans Administration Hospital near his home in the Jamaica Plain section of Boston,[16] after suffering a stroke two weeks earlier.

[15] His grandson Paul became an NHL player and referee and like his grandfather was elected to the United States Hockey Hall of Fame in 2018.