Stewart graduated from the Pasadena Playhouse.[2][3] Her first acting job was in the 1960 episode "The Glass Cage" on The Loretta Young Show.[2][4] She has guest-starred on many television series ranging from Bonanza to The Office and the recurring role of Betty Briggs on Twin Peaks.[2] She was also a prolific TV commercial actress.[3] Her notable film appearances include Eraserhead and Tremors.[2] Stewart has been married four times.[5] In 1961, she met her first husband, Tim Considine, when she played Agnes Finley in the season-one episode "Deadline" of My Three Sons.[6] They married in 1965 and divorced in 1969.[7] Her second marriage to magician Jordan Hahn lasted from the late 1970s to the early 1980s.[8][9] In 1992, Stewart married her third husband, David Banks. Following his death in 2012, she began a relationship with Michael Santos, and they married in 2015.[10]
In 2016, Stewart self-published her memoirs in a book, Little House in the Hollywood Hills.[11]