Lampert was born in New York City, the daughter of Russian Jewish immigrants Rachil Eriss, a draper and hatmaker, and Morris Lampert, an Architect and ironworker. Lampert attended New York's High School of Music & Art, and then the University of Chicago. She was married to actor Bill Alton from 1957 to 1958.

After working on minor stages for several years, including a stint as a member of the Second City troupe in Chicago, she performed on Broadway in a Tony-nominated performance in 1961's Look We've Come Through. She scored with a pair of small, noteworthy performances in the films Pay or Die and Splendor in the Grass. In the 1960s/1970s, she was active in supporting roles in film and television, and won an Emmy for her performance as a sinister gypsy on an episode of Kojak (1975). She co-starred with Gena Rowlands in John Cassavetes' Opening Night (1977).

She was a regular in the sitcom The Girl With Something Extra and the medical drama Doctors' Hospital. During the early 1970s, she originated the role of Ellie Jardin on the CBS soap Where the Heart Is until her character was killed off in 1972. In 1986, she appeared in an episode of Knight Rider (season 4, "Hills of Fire"). She worked less during the 1980s and 1990s. She appeared in The Exorcist III (playing actor George C. Scott's wife) and the offbeat 1999 film The Eden Myth.

For several years in the 1980s, Lampert appeared as the spokesperson for Goya Beans.

After a ten-year absence from films, Lampert returned to acting in supporting roles in two films: The Hungry Ghosts (2009) and Zenith (2010). In March 2010, she married broadcaster and Novelist Jonathan Schwartz in New York City.