Kellerman attended Los Angeles City College, and also enrolled in Jeff Corey's acting class. Within a year, she appeared in a production of John Osborne's "Look Back in Anger" staged by Corey and featuring classmates Shirley Knight, Jack Nicholson, Dean Stockwell and Robert Blake. Towards the end of the 1950s, Kellerman joined the newly opened Actors Studio West and debuted before the camera in the film, "Reform School Girl" (1957). To pay her tuition, Kellerman worked as a waitress at Chez Paulette.