Gates entered acting at a young age, receiving a contract with RKO at the age of 15, which required court approval because of her status as a minor. Orson Welles screen-tested her for a role in the 1942 film The Magnificent Ambersons. Although she did not get the role, which went to Anne Baxter, the test paved the way for her Future entry into film. That same year she had her first credited role, in The Great Gildersleeve. In 1943 she went on contract with RKO, her first film with them being Hitler's Children that same year. She began receiving roles in mostly B-movies, many of which were westerns or sci-fi, eventually receiving lead roles as the heroine. In 1948 she starred opposite Eddie Dean in Check Your Guns, and in 1949 she played alongside Jim Bannon, Marin Sais, and Emmett Lynn in an episode of the Red Ryder serial, titled Roll, Thunder, Roll. She would star in several other films over the next ten years, especially in westerns like Comanche Station (1959), and in support roles, most notably in two Frank Sinatra films, Some Came Running and Suddenly.