In films from early childhood, Mary McAllister became famous as "the First Baby Star of the Films," appearing in such Essanay productions as an early version of Elmer Rice's On Trial (1917) and Pants (1917). In the latter, her favorite film, she was very Mary Pickford-ish as a little rich girl masquerading as a boy. When Essanay folded in 1918, McAllister returned to school and eventually graduated from the famous Hollywood High. She embarked on a grown-up career performing in Henrik Ibsen's The Wild Duck on-stage in Los Angeles and then obtained the ingénue lead in a Norma Shearer film. The highlight of McAllisters' otherwise uninspiring adult screen career came with The Waning Sex (1926), in which she attempted to vamp the stoic Conrad Nagel. She earned a 1927 WAMPAS Baby Star title for her efforts but returned to the legitimate stage after the changeover to sound.