Her arresting performance as assassin Charlotte Corday (replacing Glenda Jackson) in the Broadway production of "Marat/Sade" in 1967 led to film offers, most notably in Medium Cool (1969) and Clint Eastwood's High Plains Drifter (1973). Her last acting film role to date was as Mary, the mother of Jesus, in the highly controversial Martin Scorsese film The Last Temptation of Christ (1988).
Bloom was the daughter of Sara (nee Damsky) and Milton Bloom, both born in Massachusetts of Russian Jewish descent. She attended Boston University's School of Fine Arts, graduating with a BFA in 1959. She worked in a coffee shop and shared a basement apartment with two other girls while studying at university. She later studied at the Herbert Berghof Studio in New York.
Went to Maine's Bar Harbour Theatre. Co-founded the Trident Playhouse in Denver and also worked as a box-office custodian, publicity chief and janitor.
She appeared in two films that have been selected for the National Film Registry by the Library of Congress as being "culturally, historically or aesthetically" significant: Medium Cool (1969) and National Lampoon's Animal House (1978).
Has one son, Sam.