While playing in Los Angeles on a touring box lacrosse team in 1937, Silverheels impressed Joe E. Brown, with his athleticism. Brown encouraged him to do a screen test, which led to his acting career. Silverheels began working in motion pictures as an extra and stunt man in 1937. He was billed variously as Harold Smith and Harry Smith, and appeared in low-budget features, westerns, and serials. He adopted his screen name from the nickname he had as a lacrosse player. Jay Silverheels was cast in a short feature film, I Am an American (1944). From the late 1940s, he played in major films, including Captain from Castile starring Tyrone Power (1947), Key Largo with Humphrey Bogart (1948), Lust for Gold with Glenn Ford (1949), Broken Arrow (1950) with James Stewart, War Arrow (1953) with Maureen O'Hara, Jeff Chandler and Noah Beery Jr., The Black Dakotas (1954) as Black Buffalo, Drums Across the River (1954), Walk the Proud Land (1956) with Audie Murphy and Anne Bancroft, Alias Jesse James (1959) with Bob Hope, and Indian Paint (1964) with Johnny Crawford. He made a brief appearance in True Grit (1969) as a condemned criminal about to be executed. He played a substantial role as John Crow in Santee (1973), starring Glenn Ford. One of his last roles was a wise white-haired chief in The Man Who Loved Cat Dancing (1973).