Kathleen Key was born Kitty Lanahan in Buffalo, New York, she debuted in films in 1920 in the film The Jackeroo of Coolabong, playing a lead role. From that point on to the end of the 1920s, Kathleen Key, sometimes credited as Kathleen Keys, starred in several films, but never really reached stardom, and was never given much credit for the roles she had, although there were some exceptions. In 1921 she played her grandmother in the short film “The Story of the Star Spangled Banner”. In 1922, she was featured in Omar Khayyam (which was not released until 1925 as A Lover’s Oath) and played a vampire in Where’s My Wandering Boy Tonight. The same year she signed to play with Charles Buck Jones in Vamoos for Fox Film. In this role she wore the dress once worn by Sara Sothern in the stage production of Smilin’ Through at the Majestic Theater in Los Angeles, California. Key spent a year in Australia as a leading woman in productions of Snow Baker around this time. Prior to making Vamoos, Kathleen Key starred with John Gilbert in St. Elmo, also for Fox. She was cast as an innocent young thing rather than playing her frequent vampire part. In 1923, as her career slowly progressed, she was selected one of the WAMPAS Baby Stars. In 1929, Key appeared in The Phantom of the North, which appeared to be her last film. However, she made three, very small and uncredited roles in 1930, 1935, and 1936, as a dance hall girl in Klondike Annie. After these minuscule appearances, Key retired from film altogether.

In the early ’30s, Kathleen Key had a well-known love affair with silent-film actor Buster Keaton, who was married at the time. As told in Keaton’s biography, the actor attempted to call off the relationship, but Key flew into a jealous rage and ransacked his MGM dressing room, which caused her to be virtually blacklisted afterward by the movie industry. It is also stated that Keaton refused to give Key a monetary loan. A telegram, sent by one of Keaton’s friends who had heard about the argument, comically read: “Congratulations. Hear you are off Key.” After her retirement in 1936, Kathleen Key spent the rest of her days in moderate comfort at the Motion Picture Country House in Woodland Hills, California, where she died at the age of 51 in 1954. Her interment was located at Valhalla Memorial Park Cemetery.