While still a student in Canada, the young Kidder wrote to director Norman Jewison who politely responded that she should give him a call if she were ever in Los Angeles. She responded by buying a plane ticket, flying to California and talking her way into an audition. Kidder made her feature debut playing a prostitute in Jewison's poorly received period newspaper comedy "Gaily, Gaily" (1969), starring Beau Bridges. She impressed the reviewer from VARIETY who wrote "Margot Kidder is Bridges' lust interest, and she's a fetching fallen angel who cries on cue and deserves better exposure, anyway you define the word." Many felt such exposure came with her very next screen appearance in "Quackser Fortune Has a Cousin in the Bronx" (1970), a warm and quirky romantic comedy set in Dublin. Kidder proved convincing as a wealthy American college girl who becomes smitten with a fellow (Gene Wilder) who sweeps up after delivery horses and sells their manure as fertilizer.
Kidder further enhanced her cult credentials with a strong performance in "Sisters" (1973), Brian De Palma's first would-be Hitchcockian thriller, as a detached Siamese twin with a murderously psychopathic sibling. That same year, Kidder followed up with another dual role in "A Quiet Day in Belfast", a little seen Canadian political drama partly filmed in Dublin. Steady work followed in films and TV as Kidder proved adept at playing kooky, eccentric or slutty. Celebrity came with "Superman" (1978) as she crafted a credible Lois Lane for 1970s Hollywood--a driven, ambitious, career woman with romantic yearnings. Despite this success, most of Kidder's subsequent non-"super" credits were less than stellar but she remained a lead for some time, playing the long-suffering co-owner of a haunted house in "The Amityville Horror" (1979); the female component of a "Jules and Jim"-like menage-a-trois in Paul Mazursky's "Willie & Phil" (1980); and a sympathetic Beverly Hills prostitute opposite embattled Vietnam vet Richard Pryor in "Some Kind of Hero" (1982).
Long plagued by mood swings and binge drinking, Kidder was first classified as manic-depressive in 1988 but rejected both the diagnosis and the treatment. Her career declined and finally crashed and burned after a 1990 car accident on the set of "Nancy Drew and Daughter", a never completed Canadian TV production. Having incurred three damaged discs in her neck but refusing surgery, Kidder was confined to a wheelchair for much of the next two years. Suits and countersuits ensued with the Canadian production company and work became scarce. She finally submitted to surgery two years later and regained the ability to walk but her insurance company would not pay for the procedure. Kidder sold her house and her jewelry and declared bankruptcy in 1992. Realizing that contemporary Hollywood had few leads for women over 40, she took small character parts where she could find them. Kidder taught acting, attempted to segue to the stage and did voice work for cartoons.
In the spring of 1996, Kidder was seen behaving erratically in public, making wild accusations and raving about a conspiracy against her before disappearing for three days. She was found hiding behind a woodpile in the backyard of a Glendale, CA, home, disheveled, dressed in rags, missing her bridgework and ranting incoherently. Suddenly the "washed-up" actress was front page news as she was confined to a county psychiatric hospital for observation. The sympathy of the world was extended to her. Old friends Christopher Reeve and Richard Pryor spoke out in her support. Broadway producer David Merrick vowed to star her in a show. Finally taking librium for her disorder and acknowledging her addictions, Kidder did a guest shot on the popular NBC sitcom "Boston Common" in the fall of 1996, which led to additional appearances later in the season.