She was born Joan Schrepfermann in Chicago, where she was also raised. She began her career as a showgirl in Chicago clubs. After appearing as a Dancer in the film The Chicago Kid (1945) and in a part in the television series Have Gun – Will Travel (1958), she moved to California around 1959. In 1959 she reprised the Lauren Bacall role of Sailor Duval in the short-lived television series Bold Venture. During the 1960s, Marshall frequently guest-starred on various television series, including Tales of Wells Fargo, Surfside 6, Hawaiian Eye, and The Jack Benny Program. She also appeared in the films Homicidal (using the stage name "Jean Arless") and Tammy and the Doctor opposite Sandra Dee and Peter Fonda.
Marshall also appeared in the 15-minute unaired pilot of The Munsters as Phoebe Munster (who strongly resembled Morticia Addams). Before the series was picked up, The Munsters was retooled and Marshall was replaced by Actress Yvonne De Carlo. Marshall continued guest-starring in episodic television throughout the 1960s before her last role in the 1975 film Shampoo with Warren Beatty.
Marshall was married twice and had two children, Steven and Sheri. Marshall married Director Hal Ashby in August 1969; the couple remained together until Ashby's death in 1988. Two years later she married executive Mel Bartfield. The couple relocated to Jamaica, where they remained until her death on June 28, 1992.