Mariclare Costello is a television, stage, and movie actress. She is a lifetime member of The Actors Studio. Costello's most notable role was Rosemary Hunter Fordwick on the television series The Waltons, from 1972 to 1977. In 1977, after her role on The Waltons, she played matriarch Maggie Fitzpatrick on the short-lived drama show The Fitzpatricks.
Her first film appearance was in The Tiger Makes Out. In 1970, she appeared on stage in "Harvey" at the ANTA Theatre, in New York City. She is also well remembered for her role as a hippie-vampire in the 1971 cult horror film Let's Scare Jessica to Death. In the 1981 Miloš Forman film Ragtime, she portrayed Emma Goldman in a scene that was ultimately deleted from the theatrical release, but still included on the DVD.
She was married to actor Allan Arbus until his death in 2013.