Her film debut was as a comical femme fatale in the Spencer Tracy and Katharine Hepburn 1949 film "Adam's Rib", directed by George Cukor. "The Asphalt Jungle" (1950) provided Hagen with her first starring role. Hagen played Doll Conover, a woman who sticks by criminal Dix's side until the bitter end. She appeared in the film noir "Side Street" (1950), playing a gangster's sincere but dim girlfriend. Hagen had a comic performance in "Singin' in the Rain" as the vain and talentless silent movie star Lina Lamont. She received an Academy Award nomination for Best Supporting Actress for her performance.