He had a nine-season (1941–1942; 1948–1954) career in Major League Baseball as an outfielder and pinch hitter for the Pittsburgh Pirates, New York Yankees, Washington Senators and Chicago White Sox.

Stewart batted left-handed, threw right-handed, stood 5 feet 11 inches (1.80 m) tall and weighed 160 pounds (73 kg).

While Williams moved on to a Hall of Fame career in the Majors, Stewart remained with the Padres until October 1, 1940, when he was purchased by the Pirates.

After spending 1947 with the Kansas City Blues of the American Association, he began the 1948 season with the Yankees as a teammate of Joe DiMaggio.

During and after his playing days, he was a physical education instructor in Hawthorne, California, and appeared as an extra in several Hollywood films.