She was the second Superman actor to work on the series Smallville, following in the footsteps of Christopher Reeve, who played Virgil Swann on the series. Margot's character was killed off the show after she refused to be the one who announced Swann's death, as she believed it was "distasteful" to do it so soon after Reeve's real-life death.
She is the aunt of actress Janet Kidder. They have worked together only once, on the episode Walk on By of the popular spy series La Femme Nikita. In the episode, Margot and Janet play older and younger versions of the same character.
Outside the acting world, she runs a charity for mental wellness and campaigns with pro-choice groups across the USA and Canada.
She doesn't believe in superstition and "Hollywood legends", believing the events that were the basis for her movie The Amityville Horror were works of fiction, and that the supposed "Superman curse" that plagued many Superman stars, which included Christopher Reeve, Richard Pryor, Marlon Brando and herself, was all coincidence.
She has appeared in productions of The Vagina Monologues, appearing at New York's Westside Theatre in 2002 and Vancouver's Vogue Theatre in 2001.
She has been romantically linked to Pierre Trudeau, the former Prime Minister of Canada.
She became a United States citizen on August 17, 2005.
She suffers from bipolar disorder.
In 1996, she had a complete mental breakdown. Whilst already suffering from manic depression, she became increasingly paranoid, claiming that her first husband was trying to kill her and believing she was suffering from deadly diseases. In desperation, she ran away from home, cut off all her hair with a razor blade, lived on the streets and faked her own death. Thankfully, one of her old friends found her sleeping in her backyard and Margot was sent to a psychiatric hospital. An intervention took place and she eventually recovered.
Noted director Brian De Palma offered her the role of Carrie White in the horror classic Carrie but she turned it down. At the time, she had already made three horror movies and was about to start filming her fourth, and was keen to pursue work in other genres.
She is prone to injury, having been restrained to a chair for two years following a car accident in 1990 and breaking her pelvis due to a car crash in 2002.
She won the Best Actress award for A Quiet Day In Belfast at the 1975 Canadian Film Awards.
She turned down the opportunity to have a cameo role in the 2006 remake of Black Christmas, in respect of her work in the 1974 original.
She briefly dated director Brian De Palma in the early '70s. As a Christmas present, he offered her the lead role in his movie Sisters, which raised her profile in Hollywood.
Her screentime as Lois Lane was drastically cut during the sequel Superman III, as she had publicly expressed disgust at Warner Bros. for firing the original director of Superman II, Richard Donner.
She has one daughter, Maggie, who was born in 1976.
She has been married three times. Her first marriage (1975-1976) was to scriptwriter Thomas McGuane, her second (1979) to actor John Heard, and her third (1983-1984) to French director Philippe de Broca.
She lived with another aspiring actress, Jennifer Salt, in her early days in Los Angeles and the two remain best friends to this day. Salt is now a writer on the cable series Nip/Tuck, which happens to be Margot's favorite show.
She first became interested in acting as a child, when she felt a need to express herself. At boarding school, she took part in several school plays, including a leading role in their production of Romeo and Juliet.
Is strong and moderate in her political beliefs.
She played Lois Lane in the Superman movies. She appeared on Smallville in the fourth season, just as Lois Lane entered the series.