Most recently, Margot appeared in The Neighbourhood, which came out earlier this year.
The actress found fame starring alongside Christopher Reeve in the Superman films of the 1970s and 1980s.
Born Margaret Ruth Kidder on October 17, 1948 in Canada's Northwest Territories, she grew up in a small town without a movie theatre.
She also appeared in the film The Great Waldo Pepper and the children's TV series RL Stine's The Haunting Hour.
Kidder suffered from bipolar disorder, according to People Magazine, which often caused episodes of erratic behavior that landed her in the tabloids with some frequency. The Canadian-born actress had always been open about drug and alcohol addictions, which she said partially triggered her very public breakdown in 1996.
Five ambulances were also called in seven months. "She was really a blazing energy".
If you or someone you know is dealing with suicidal thoughts, you can call the National Suicide Prevention Lifeline at: 1-800-273-8255.