She became a household name after Superman was a massive box office hit in 1978.
Reeve died in 2004 of complications from an infection, nine years after becoming a quadriplegic following a horse riding accident.
Margot candidly spoke out about her battle with bipolar disorder, which she suffered for years.
The later stages of Kidder's life were lived in stark contrast to her days in Hollywood during the '70s and '80s, with the actress describing herself to The Guardian in 2005 as "a grandmother with my dogs and nice friends here in the Rocky mountains". Police responded to the call and found Margot Kidder unresponsive. She rose to prominence in the American filmmaking scene when she was cast as the eponymous Siamese twins in Brian De Palma's Sisters (1973), which presaged a career in 1970s horror and genre films.
She'd been married 3 times, although she'd been single since the '80s.More news: Republican governors back Trump's nomination for Nobel peace prize
She was also known for her work as a mental health advocate. Her father was the manager of the Yellowknife Telephone Company from 1948 to 1951.
In 2001, she played the abusive mother of a serial killer on Law & Order: Special Victims Unit.
She was unable to work for two years after serious vehicle crash in 1990.
Marvel Studios President Kevin Feige called the moment "the best cinematic superhero save in the history of film" at an Academy of Motion Picture Arts and Sciences event honouring Donner a year ago. Her first major studio film was 1969's Gaily, Gaily, a comedy that starred Beau Bridges.
Kidder is seen here with Carrie Fisher, as the two attended a fundraiser in 1980 at the Empire State Building in New York City. The two had a brief romance on the movie. She later appeared in Sisters, The Great Waldo Pepper with Robert Redford and 1979 horror-flick The Amityville Horror.
She is survived by Maggie, 41, her daughter with first husband, novelist Thomas McGuane.
Kidder and Reeve went on to star in three more Superman movies, the fourth and last in 1987. For fans of Yuletide terror, she memorably played the "bad girl" Barb in Black Christmas (1974).