Born Margaret Nixon McEathron in Altadena, California to Charles Nixon and Margaret Elsa (née Wittke) McEathron, Marni Nixon, a child actress, also began singing at an early age in choruses, including performing solos with the Roger Wagner Chorale.

She went on to study singing and opera with Carl Ebert, Jan Popper, Boris Goldovsky and Sarah Caldwell. She embarked on a varied career, involving film and musical comedy as well as opera and concerts. She appeared on American television, dubbed the singing voices of film actresses in The King and I, West Side Story and My Fair Lady, and acted in several commercial stage ventures.

Under her own name, she has also recorded songs by Jerome Kern, George Gershwin, Arnold Schönberg, Charles Ives, Aaron Copland and Anton Webern. Nixon received two Grammy Best Classical Performance, Vocal Soloist nominations, one for her Schönberg album and one for her Copland album.