Polley was born in Toronto, Ontario, the youngest of five children born to Diane Elizabeth (née MacMillan), an actress (Street Legal) and casting director, who died of cancer the week of Polley's 11th birthday. Polley was raised by Diane and her second husband, Michael Polley, a British-born actor who became an insurance agent after Diane and he started a family. Her siblings are Mark and Joanna, both older, and, from her mother's first marriage, Susy and John Buchan. Her mother Diane had Scottish ancestry.
During her childhood, Polley's siblings teased her because she bore no physical resemblance to Michael. Polley discovered as an adult that her biological father was actually Harry Gulkin, with whom her mother had had an affair (as chronicled in Polley's film Stories We Tell). Gulkin, the son of Russian-Jewish immigrants, is a Quebec-born film producer who produced the 1975 Canadian film Lies My Father Told Me, and had met Diane after attending a play in which she acted in Montreal in 1978.
When Polley turned 18, she decided to follow up on suggestions from her mother's friends that her biological father might be Geoff Bowes—one of three castmates from her mother's play in Montreal. Meeting with Gulkin as just someone who could provide information about Diane in Montreal, he informed Polley of his affair with Diane. Bowes and Michael Polley also confirmed, in Stories We Tell, that they had sexual relations with Diane during the run of the Montreal play. Gulkin's paternity was later confirmed by a DNA test.
Polley attended Subway Academy II, then Earl Haig Secondary School, but dropped out at age 15.
Her first cinematic appearance was at the age of four, as Molly in the Disney film One Magic Christmas. She was also in the pilot episode for Friday the 13th – The Series, as well as appearing in a small role in William Fruet's sci-fi horror film Blue Monkey , both in 1987. At age eight, she was cast as Ramona Quimby in the television series Ramona, based on Beverly Cleary's books.
That same year, she played one of the lead characters in Terry Gilliam's The Adventures of Baron Munchausen. Polley burst into the public eye the following year, 1990, as Sara Stanley on the popular CBC television series Road to Avonlea. The series made her famous and financially independent, and she was hailed as "Canada's Sweetheart" by the popular press.
The show was picked up by the Disney Channel for distribution in the United States. At the age of 12 (around 1991), Polley attended an awards ceremony while wearing a peace sign to protest the first Gulf War. Disney executives asked her to remove it, and she refused. This soured her relationship with Disney, though she continued on Road to Avonlea until 1994. The show ran until 1996, although Polley did return as Sara Stanley for an episode in 1995 and for the series finale.
Polley appeared as Lily on the CBC Television series Straight Up. It ran from 1996–1998 and she won the Gemini Award for Best Performance in a Children's or Youth Program or Series for her role. Polley's subsequent role as Nicole Burnell in the 1997 film The Sweet Hereafter, brought her considerable attention in the United States; she was a fan favourite at the Sundance Film Festival. Her character in the film was an aspiring singer — on the soundtrack, she performed a cover of The Tragically Hip's "Courage" and Jane Siberry's "One More Colour", as well as the film's title track which she co-wrote with Mychael Danna. "Courage" was also played in the ending of an episode of Charmed, "Long Live the Queen" (season 4 episode 20). Polley appeared in two critically acclaimed small movies, 1998's Last Night and the well-received 1999 film Go with budding actress Katie Holmes, to end the 1990s.
She was cast in the role of Penny Lane in the big-budget 2000 film Almost Famous, but dropped out of the project to return to Canada for the low-budget The Law of Enclosures. Her role in the 2003 film My Life Without Me garnered the Genie Award for Best Performance by an Actress in a Leading Role in 2004. In the same year, she starred in a lead role in the remake of Dawn of the Dead, which was a departure from her other indie roles.
In 2005, she starred in The Secret Life of Words, opposite Tim Robbins and Julie Christie. She was nominated as Best European Actress by the European Film Academy for her role as Hanna.
In 2006, Polley took a role on the acclaimed series Slings and Arrows during its third and final season. Polley's father, Michael Polley, was a regular on the show during its entire three-season run. She served as a member of the 2007 Cannes Film Festival jury.
In 2008, Polley appeared as Nabby Adams in the HBO miniseries based on the life of John Adams. Polley played Elise in Jaco Van Dormael's Mr. Nobody, which was released in 2010. Critical response has praised the film's artistry and Polley's acting. Later that year, she also appeared in a cameo role in Bruce MacDonald's film Trigger.
In 1999, Polley made her first short film, The Best Day of my Life, for the On the Fly 4 Film Festival. She also made a second short film that year, Don't Think Twice. Polley attended the Canadian Film Centre's directing program in 2001, and won the Genie Award for Best Live Action Short Drama in 2003 for her short film I Shout Love.
She made her feature-length film directing debut with Away from Her, which Polley adapted from the Alice Munro short story The Bear Came Over the Mountain. The movie, starring Julie Christie (with whom she had played in No Such Thing, 2001, and The Secret Life of Words, 2005), debuted at the Toronto International Film Festival on September 11, 2006, as part of the TIFF's Gala showcase.
Away from Her was acquired by Lionsgate for release in the US for the sum of $750,000. It drew rave reviews from Variety, The Hollywood Reporter, and the three Toronto dailies, both for the performances of Christie and her co-star, Canadian actor Gordon Pinsent, and for Polley's direction. It also earned Polley a 2007 Academy Award nomination for Best Adapted Screenplay, and won the Genie Award for Best Achievement in Direction. At the 2008 Genies, she was also awarded the Claude Jutra Award, which recognizes outstanding achievement by a first-time feature film director.
Polley wrote and directed her second feature, Take This Waltz starring Michelle Williams, Luke Kirby, Seth Rogen, and Sarah Silverman, which premiered at the Toronto International Film Festival in 2011.
In 2012, her documentary film Stories We Tell premiered at the 69th Venice International Film Festival in competition in the Venice Days category. The critically acclaimed documentary examined family secrets in Polley's own childhood. Also in 2012, Polley announced that she would be adapting Margaret Atwood's novel Alias Grace. In August 2014, during a profile of her work as a director, Polley announced that Alias Grace was being adapted into a six-part miniseries. In June 2016 the series was confirmed with Polley writing and producing the six-part miniseries which will air on CBC Television in Canada and will stream on Netflix globally.
In June 2014, it was announced that she would be writing and directing an adaptation of John Green's Looking for Alaska. In 2015, it was announced that due to scheduling conflicts, Polley would no longer be directing the film.
In an interview, Polley stated that she takes pride in her work and enjoys both acting and directing, but is not keen on combining the two:
I like the feeling of keeping them separate. I find that really gratifying. I can't imagine combining those. For me, I love the feeling of using different parts of my brain separately.
Political and social activism
Following the row with Disney, Polley dedicated more of her efforts to politics, becoming a prominent member of the Ontario New Democratic Party (ONDP), where Ontario legislator Peter Kormos was her political mentor. In 1996, she gave a nomination speech for Kormos at the ONDP leadership convention which she later referred to as the "proudest moment in [her] life".
In 1995, she lost two back teeth after being struck by a riot police officer during a protest against the Provincial Progressive Conservative government of Mike Harris in Queen's Park. She was subsequently involved with the Ontario Coalition Against Poverty. She has recently scaled back her political activism. She was part of a group in 2001 which opposed the proposed Free Trade Area of the Americas. The 3rd Summit of the Americas was held in Quebec City in April 2001. In 2003, she was part of former Toronto mayor David Miller's transition advisory team.
In 2009, Polley directed a two-minute short film in support of the Heart and Stroke Foundation of Canada. In advance of the film's airing in Canada during the 82nd Academy Awards, and following news reports that characterized the film as a marketing exercise for the margarine company Becel, Polley withdrew her association with the film. "In December 2009, I made a film to be aired during the Academy Awards that I believed was to promote the Heart and Stroke Foundation.
When I agreed to make this film ["The Heart"], I was thrilled, as I was proud to be associated with the work of this incredible organization. However, I have since learned that my film is also being used to promote a product. Regretfully, I am forced to remove my name from the film and disassociate myself from it. I have never actively promoted any corporate brand, and cannot do so now." In response, Becel said it was a "founding sponsor" of the Heart Truth campaign and had commissioned the film "to put heart health on the radar of Canadian women".
In January 2012, Polley endorsed Toronto MP Peggy Nash in the 2012 New Democratic Party leadership race to succeed Jack Layton.
Polley is an atheist. On September 10, 2003, she married Canadian film editor David Wharnsby, her companion of seven years. They divorced in 2008.
In 2007, Polley discovered that the man who raised her was not her biological father. The story of her mother's affair and her biological father are detailed in her documentary Stories We Tell.
On August 23, 2011, she married David Sandomierski, who is working on his PhD in law at the University of Toronto. Their daughter Eve was born on February 7, 2012. In August 2014, Polley revealed that she had given birth to a second daughter.
On October 16, 2010, it was announced that she would receive a star on Canada's Walk of Fame. In June 2013, she received the National Arts Centre Award recognizing achievement over the past performance year at the Governor General's Performing Arts Awards, where she was the subject of a short vignette by Ann Marie Fleming entitled Stories Sarah Tells. Polley was appointed an Officer of the Order of Canada on December 30, 2013.ACTRA2006 – ACTRA Toronto Award of Excellence (Won)Academy Awards2008 – Best Adapted Screenplay, Away from Her (Nominee)Gemini Awards2007–Best Performance by an Actress in a Featured Supporting Role in a Dramatic Series, Slings and Arrows (Nominated)1998–Best Performance in a Children's or Youth Program or Series, Straight Up (Won)1998–Best Performance by an Actress in a Featured Supporting Role in a Dramatic Program or Mini-Series, The Planet of Junior Brown (Nominated)1998–Best Performance by an Actress in a Leading Role in a Dramatic Program or Mini-Series, White Lies (Nominated)1994–Best Performance by an Actress in a Continuing Leading Dramatic Role, Road to Avonlea (Nominated)1993–Best Performance by an Actress in a Continuing Leading Dramatic Role, Road to Avonlea (Nominated)1992–Best Performance by an Actress in a Supporting Role, Lantern Hill (Won)1990–Best Performance by an Actress in a Continuing Leading Dramatic Role, Road to Avonlea (Nominated)1988–Best Performance by an Actress in a Continuing Leading Dramatic Role, Ramona, (Nominated)Genie Awards2008–Claude Jutra Award, (Special Prize)2008–Best Director, Away from Her, (Won)2008–Best Adapted Screenplay, Away from Her, (Won)2004–Best Performance by an Actress in a Leading Role, My Life Without Me, (Won)2003–Best Live Action Short Drama, I Shout Love (Won)2002–Best Performance by an Actress in a Leading Role, The Law of Enclosures (Nominated)1997–Best Original Song, The Sweet Hereafter, (Nominated)1997–Best Performance by an Actress in a Leading Role, The Sweet Hereafter, (Nominated)Independent Spirit Awards2000–Best Supporting Female, Go, (Nominated)Toronto Film Critics Association Awards2012–Rogers Canadian Film Award and Best Documentary Film Award, Stories We TellWriters Guild of America Award for Best Documentary Screenplay2014–Stories We Tell