Mary Lee's first screen appearance was with Warner Bros., in Nancy Drew.. Reporter (released 18 February 1939) where she portrayed Mary Nickerson, the younger sister of Nancy Drew's (Bonita Granville) boyfriend, Ted Nickerson (Frank Thomas, Jr.).
Her other films included Rancho Grande, Ride, Tenderfoot, Ride, Sing, Dance, Plenty Hot, Carolina Moon and Gaucho Serenade.