Mitchell started out as a stage Actress, and gained a foothold in television with a number of appearances in popular shows in the 1960s. In 1970, she got her first leading TV role, as Ruth, the daughter of the title character (Irene Handl) in the gentle comedy For the Love of Ada, which ran for four series and 27 episodes, followed by a spin-off film. At the same time, she was appearing periodically as Mrs. Abbott, the absurdly over-protective mother of would-be tough guy Frankie ("Mummy's little soldier"), in Please Sir! and its sequel The Fenn Street Gang. Mitchell's appearances as Mrs. Abbott were sporadic, and fleeting, but were hugely popular and are still remembered with affection.