After a highly publicized manic episode and nervous breakdown in 1996, Kidder's career began to slow. By the 2000s, however, she had maintained steady work in independent films as well as television, with guest-starring roles on Smallville, Brothers & Sisters, and The L Word. In 2015, she won an Emmy Award for her performance on the children's television series R.L. Stine's The Haunting Hour. She has also acted in theatrical productions, most notably appearing on Broadway in a 2002 production of The Vagina Monologues.
In 2005, Kidder became a naturalized U.S. citizen. She is an outspoken political, environmental, and anti-war activist. She has also advocated the use of orthomolecular medicine, which she credits as having helped treat her bipolar disorder.
Kidder, one of five children, was born in Yellowknife, Northwest Territories, the daughter of Jocelyn Mary "Jill" (née Wilson), a history teacher, and Kendall Kidder, an explosives expert and engineer. Kidder also spent time growing up in Labrador City, Newfoundland and Labrador. Her mother was from British Columbia, Canada, and her father was from New Mexico, United States. She is of Welsh and English descent. Kidder was born in Yellowknife because of her father's job, which required the family to live in remote locations. Her father was manager of the Yellowknife Telephone Company from 1948 to 1951. Kidder recalled her childhood in northern Canada, saying, "We didn't have movies in this little mining town. When I was 12 my mom took me to New York and I saw Bye Bye Birdie, with people singing and dancing, and that was it. I knew I had to go far away. I was clueless, but I [have done] okay."
Kidder attended multiple schools in her youth, and graduated from Havergal College, a boarding school in Toronto, in 1966. She has a sister, Annie, and three brothers, John, Michael and Peter. Kidder's niece, Janet Kidder, is also an actress.
Kidder made her film debut in a 49-minute film titled The Best Damn Fiddler from Calabogie to Kaladar (1968), a drama set in a Canadian logging community, which was produced by the Challenge for Change. Her first major feature was the 1969 American film Gaily, Gaily, a comedy starring Beau Bridges. She appeared in a number of TV drama series for the CBC, including guest appearances on Wojeck, Adventures in Rainbow Country, and a semi-regular role as a young reporter on McQueen, and as a panelist on Mantrap which featured discussions centered on a feminist perspective. During the 1971–72 season, she co-starred as barmaid Ruth in Nichols, a James Garner western, which aired 22 episodes on NBC.
In the late 1960s, Kidder was based in Toronto, and in 1970, relocated to Vancouver. During an August 3, 1970 interview on The Dick Cavett Show, Kidder stated that she was ambivalent toward having a film career, and was considering working as a film editor in the future. She appeared in "Such Dust As Dreams Are Made On", the first pilot for Harry O which aired in March 1973. She was a guest star in a 1972 episode of the George Peppard detective series Banacek.
After moving to Los Angeles, Kidder was cast opposite Gene Wilder in Quackser Fortune Has a Cousin in the Bronx (1970) as an exchange student in Ireland who becomes the love interest of a poor horse manure collector in Dublin whom she almost runs over with her car. After filming in Ireland, Kidder relocated to New York City to further study acting. A year later, she returned to California, and was cast in the Brian De Palma cult classic Sisters (1973), which gained notoriety for both director and Kidder, who as leading lady, portrayed conjoined twins. Kidder had been in a relationship with De Palma at the time, and had been roommates with co-star Jennifer Salt in Los Angeles. She then starred in the slasher film Black Christmas in 1974, for which she won a Canadian Film Award for Best Actress; followed by a role as a prostitute in the Terrence Malick-scripted The Gravy Train (1974). She received another Canadian Film Award for Best Actress for her performance in the war drama A Quiet Day in Belfast (1974).
In 1975, Kidder was cast in a lead role in The Great Waldo Pepper opposite Robert Redford, she also appeared in The Reincarnation of Peter Proud and 92 in the Shade (1975) with Peter Fonda, all of which established her as a commercially viable leading lady. Kidder famously married the director of 92 in the Shade, Thomas McGuane. She appeared on the March 9, 1975 edition of The American Sportsman, learning how to hang glide with her providing the narration and a remote microphone recording her reactions in flight; the segment concluded with Kidder doing solos soaring amid the Wyoming Rockies.
After taking a break from acting after the birth of her daughter in 1976, Kidder sought to return to making films in the late 1970s. After doing a reading of Lois Lane for the 1978 superhero film Superman: The Movie, Kidder was flown to England by Richard Donner for screen-tests. Donner ultimately cast Kidder in the role, which would become her most iconic. Filming took over a year, and the film was released during Christmas 1978, to major commercial success. Kidder won a Saturn Award for best actress for her performance in the film. Kidder publicly disagreed with the decision of producers Alexander Salkind and Ilya Salkind to replace Richard Donner as director for Superman II (1980). It was reported that as a result, Kidder's role in Superman III (1983) consisted of less than five minutes of footage, though the producers have denied this in DVD commentaries. Her role in Superman IV: The Quest for Peace (1987) was more substantial.
Kidder's performance as Kathy Lutz in the 1979 summer release of The Amityville Horror further cemented her status as one of Hollywood's leading ladies. Though it received mixed reviews from critics, The Amityville Horror was a major commercial success, grossing over $86 million in the United States. Janet Maslin of The New York Times, though giving the film a mixed review, said Kidder "stubbornly remains the bright-eyed life of the party [in the film]." In retrospect, Kidder called the film "a piece of shit." The same year, Kidder hosted an episode of the American sketch comedy TV show Saturday Night Live.
Kidder continued to work in film throughout the 1980s, appearing in Paul Mazursky's Willie & Phil and Some Kind of Hero. Her performance in 1981's Heartaches generated critical acclaim and Oscar buzz. As court stenographer-cum-private eye Mickey Raymond, the PG rating that 1983's Trenchcoat received led Disney to launch Touchstone Pictures. She appeared opposite James Garner in the controversial Hollywood crime drama The Glitter Dome (1984). In 1985, she toplined Little Treasure for Columbia Tri-Star with co-stars Ted Danson and Burt Lancaster, where she played a distraught stripper looking for her bank robber-father's buried fortune. In 1986 she was selected as the English narrator for the Japanese animated series The Wonderful Wizard of Oz.
A 1982 stage performance of Bus Stop starring Kidder as Cherie and Tim Matheson as Bo, was broadcast on HBO. In 1983, she produced and starred as Eliza Doolittle in a version of Pygmalion with Peter O'Toole for Showtime. She produced and starred in the French-Canadian period television film Louisiana (1984) as a plantation owner in the American South who returns from Paris to find her estate and holdings have been lost. Body of Evidence (1988), a CBS Movie of the Week, cast Kidder as nurse who is suspicious that her medical pathologist second husband is a serial killer. In 1994, Kidder played the bartender at the Broken Skull Tavern in Under a Killing Moon, an IBM PC adventure game. In 1994 she took time to appear in the Disney Channel movie WindRunner, with Russell Means and Jason Wiles. She made uncredited cameo appearances in Maverick (1994) and Delirious (1991).
By the mid-1990s, Kidder's career began to decline, which was attributed to her widely publicized nervous breakdown in 1996.
In 2000, Kidder played Eileen Canboro in Apocalypse III: Tribulation, a Christian film dealing with Christian eschatology and the Rapture. Kidder stated afterwards that she did not realize until she was on the set that the movie was serious. In 2001, she played the abusive mother of a serial killer in "Pique", an episode of Law & Order: Special Victims Unit. In 2002, she appeared alongside Crispin Glover and Vanessa Redgrave in the film adaptation of Crime and Punishment.
Kidder appeared on Broadway in The Vagina Monologues in December 2002, and toured with the show for two years. After this, she appeared on Robson Arms, a Canadian sitcom set in an apartment block in Vancouver's west end. She played a quirky neighbor of the main cast members. She also had a cameo in Rich Hall's Election Special on BBC Four. In 2006, Kidder played Jenny Schecter's mother Sandy Ziskin on The L Word, a repressed Jewish woman coming to terms with her daughter's sexuality. In 2007, Kidder began appearing on the television series Brothers and Sisters, playing Emily Craft. In 2004, Kidder briefly returned to the Superman franchise in two episodes of the television series Smallville, as Dr. Bridgette Crosby, an emissary of Dr. Swann (played by her Superman co-star, Christopher Reeve).
She portrayed an embattled guidance counselor in the 2008 gay-themed mystery film On the Other Hand, Death, as well as a supporting role as Laurie Strode's therapist, in Rob Zombie's Halloween II (2009). In an interview with the LGBT publication The Advocate, Kidder discussed her later career choices, saying: "I’m not choosy at all! I’ll do practically anything. I’m the biggest whore on the block. I live in a little town in Montana, and you have to drag me out of here to get to L.A., so I’m not readily available. But unless it’s something sexist or cruel, I just love to work. I’ve done all sorts of things, but you just haven’t seen them because they’re often very bad and shown at 4 in the morning."
In 2015 Kidder won an Emmy award for Outstanding Performer in Children's Programming for her performance in R.L. Stine's The Haunting Hour.
Kidder dated former Canadian prime minister Pierre Trudeau, director Brian De Palma, and actor/comedian Richard Pryor. She has been married and divorced three times. Kidder's first husband was American novelist Thomas McGuane, with whom she had her only child, daughter Maggie McGuane, born in 1976. She was married to actor John Heard in 1979 for only six days, and was married to French film director Philippe de Broca from 1983 to 1984. Since her divorce from De Broca, she has said that she prefers the companionship of her dogs. Kidder has two grandchildren from her daughter Maggie's marriage to novelist Walter Kirn.
She maintained a close friendship with her Superman co-star Christopher Reeve, which lasted from 1978 until his death in 2004. "When you're strapped to someone hanging from the ceiling for months and months, you get pretty darned close," Kidder told CBS. "He was such a huge part of my life... He was complicated, very smart, really smart, and he knew he'd done something meaningful. He was very aware of that and very happy with that role."
Kidder was in a car crash in December 1990, after which she was unable to work for two years, causing her financial problems.
Kidder stated in an interview with TV Guide that she is an atheist.
Kidder has been diagnosed with bipolar disorder, which was the cause of a widely publicized manic episode that she experienced in April 1996. At the time, Kidder had been working on an autobiography, when her laptop computer was infected with a virus, which caused it to crash and her to lose three years' worth of drafts. Kidder flew to Los Angeles to have the computer examined by a data retrieval company, who ultimately were unable to retrieve the files. Kidder then entered a manic state and disappeared for four days. She was found in a backyard by a homeowner and was taken by the Los Angeles Police Department to Olive View Medical Center in a distressed state, the caps on her teeth having been knocked out during a purported rape attempt. She was later placed in psychiatric care. In 2007, Kidder said that she had not had a manic episode in 11 years, and has credited her well-being to orthomolecular medicine.
Kidder has been a longtime supporter of Democratic and liberal causes throughout her career. She has credited her interest in politics to conversations her parents would have over the dinner table during her childhood; her mother was Canadian with socialist leanings, while her father was originally from the United States, and was a conservative Republican.
She actively supported Jesse Jackson's bid for the Democratic nomination in the 1984 U.S. presidential election. In the early 1990s, during the first Gulf War, Kidder was branded a "Baghdad Betty" and subjected to abuse for her remarks questioning the war. In a piece called "Confessions of 'Baghdad Betty'", styled as a letter to her mother and printed in The Nation, Kidder responded by explaining and defending her statements.
As of November 2009, Kidder was the Montana State Coordinator for Progressive Democrats of America. The organization's website carried her article "Ax Max", in which she criticized Max Baucus, Montana's Democratic senator. On August 23, 2011, Kidder, Tantoo Cardinal, and dozens of others were arrested while protesting in Washington D.C. against the proposed extension of the Keystone Pipeline. In 2012, she appeared in a video for Stop the Frack Attack, an environmental organization working toward regulating fracking practices. When discussing sustainable energy, Kidder said: "The first thing people have to start facing, contrary to the advertising fed to us by oil and gas companies, is that environmentalism and economic stability go hand-in-hand on any long term basis."
On August 22, 2015, Kidder was named the host of a dinner event by the Yellowstone County Democrats in Billings, Montana called "Billings for Bernie" in support of Bernie Sanders' presidential primary bid.
She has contributed articles to CounterPunch, a left-wing magazine, beginning in 2009. In an article expressing her reaction to the 2016 Democratic National Convention, she wrote, "I am not an American tonight... I reject the words I voiced at my citizenship ceremony."
In addition to her campaigning in the United States, Kidder has expressed support for liberal causes in Canada. In 2011, she supported her brother, John Kidder, in Vancouver, who was running to be a member of Canada's Parliament. :
I'm here not only because John is a dream candidate but because I'm living in the end game in the United States and it's not funny. Canada is starting the same sort of right-wing, corporate ownership of government, corporate tradeoffs with government, smear campaigns, `let's lower the corporate tax rate without mentioning it's going to up the private tax rates' It's happening in Canada. God forbid if anyone should bring up privatizing health care.
Kidder became a United States citizen on August 17, 2005, in Butte, Montana; she lives in Livingston, Montana. She said that she decided to become an American citizen to participate in the voting process, to continue her protests against U.S. intervention in Iraq, and to be free of worries about being deported.