Polley was born into a showbusiness family: her father, Michael, an emigrant from England who had gone to acting school with Albert Finney, appeared with her in the movie The Adventures of Baron Munchausen and on the television series Road to Avonlea, and her mother, Dianne, was an actress and casting director. It was her mother’s connections that launched Sarah, at her own insistence, on an acting career at the age of four, following in the footsteps of her older brother Mark. While Mark is no longer in show business, another brother, John Buchan, is a casting director and producer.
Her career as a child actress shifted into high gear when she was cast as the Cockney waif Jody Turner in Lantern Hill, (1991) for which she won a Gemini Award, the Canadian equivalent of the Emmy, for Best Performance by an Actress in a Supporting Role in 1992. Produced by Kevin Sullivan, the film was based on the book by Lucy Maud Montgomery, author of Anne of the Green Gables. When Sullivan created a television series based on Montgomery's work, he cast Polley in the lead role of Sara Stanley in Road to Avonlea. The series propelled Polley into the first rank of Canadian TV stars and made her independently wealthy by the age of 14.
Polley's personal life was deeply affected by the death of her mother Diane from cancer shortly after her 11th birthday, a development that ironically paralleled the fictional life of her character Sara. Highly intelligent and politically progressive at a young age, Polley eventually rebelled against what she felt was the Americanization of the series after it was picked up by the Disney Channel for distribution in the U.S. She eventually dropped out of the show. Her disenchantment with the series also may have had its roots with her poor relationship with Disney. During the Gulf War, when she was 12 years old, Polley was sitting with Disney executives at a children's awards show and was asked to remove a peace sign that she was wearing. Polley refused and apparently was blacklisted by Disney. Though Polley does not blame her parents, she remains publicly disenchanted over the loss of her childhood and in October 2003 said she is working on a script about a 12-year old girl on a TV show.
Polley, who picked up a second Gemini Award for her performance as the Goth Lilly in the TV series Straight Up, subsequently dropped out of acting and high school to turn her attention to politics, positioning herself on the extreme left of Canada's left-of-center New Democratic Party. The publicity ensuing from her losing some teeth after being slugged by an Ontario policeman during a protest against the Conservative provincial government, plus the stinging cynicism from some other activists unimpressed by her "celebrity," led Polley to a decision to lower her political profile and return to acting in the role of Nicole in director Atom Egoyan's film The Sweet Hereafter.
It was her appearance as Nicole, the teenage girl injured in a school bus accident who serves as the conscience of the small town rent by the tragedy, that first brought Polley to the attention of critics in the U.S. In her native Canada, the role was heralded by critics as her successful breakthrough to adult roles. It was Polley's second film with Egoyan, who wrote the part with her in mind when he adapted Russell Banks' novel. Predictions of an Academy Award nomination and future stardom were part of the critical consensus, and Polley received her first Best Actress nomination from Canada's Academy of Canadian Cinema & Television and the Best Supporting Actress from the Boston Society of Film Critics. The publicity crested at the Sundance Festival, where her starring role in the film Guinevere (1999) was showcased, when the entertainment media crowned her the "It Girl" of 1999.
Intensely private, and extremely ambivalent about the personal cost of celebrity and the Hollywood ethos "Fame is the Name of the Game," Polley could be seen as rebelling against the expectations of mainstream cinema when she embarked a career path that took her out of the spotlight thrown by the harsh lights of the Hollywood hype/publicity machine. Polley dropped out of Cameron Crowe's Almost Famous, the $60-million mega-hyped vehicle that was supposed to make her a mainstream star in the U.S., choosing to return to Canada to make the $1.5 million The Law of Enclosures (2001) for Genie Award-winner John Greyson, a director she greatly admires. The film grossed poorly in Canada and was not released in the U.S., but it did win recognition from critics and garnered Polley her second Genie nomination for Best Actress. Her replacement in Almost Famous, meanwhile, went on to an Oscar nomination and a career above the title in glossy Hollywood films. In contrast, Polley took a wide variety of parts, large and small, in independent films, including significant roles in the ensemble pieces The Claim (2000) and The Weight of Water (2000), bit parts in eXistenZ(1999) and Love Come Down (2000) and the lead in No Such Thing (2001). Her choice of projects showed her to be a questing spirit more focused on learning the art of her craft than on stardom.
Polley has said that her choice of film roles, eschewing mainstream Hollywood movies for chancier, non-commercial independent fare, was the result of an ethical decision on her part to make films with a social import. A less observant viewer might think that the rebel Polley played in her political life and that had previously manifested itself in her professional life was now driving her to the verge of career suicide in terms of popularity, marketability and choice of future roles. However, that interpretation does not recognize the extraordinary talent that will always keep her in demand by directors, if not casting agents with an eye on the opening weekend box office. One must understand Polley's career progression in light of her attendance at the Canadian Film Centre's directors program and her production of short films, including "Don't Think Twice" (1999) and the highly praised "I Shout Love" (2001). Polley is a cinema artist. This woman wants to, and will, make films. Thus, we can understand her career choices as a desire to work and understand the technique of some of the best directors in film, including David Cronenberg, Michael Winterbottom and Hal Hartley.
Polley is as renowned for her intelligence as for her remarkable talent. The problem of the intelligent person in the acting field, as we can see from the tragic case of Richard Burton, is that the actor, as artist, in not ultimately in control of their medium, and it is control that is the hallmark of the great artist. The controlling intelligence on a movie set is the director, and her attendance at the Canadian Film Centre has given Polley a new perspective on acting. The actor, she says, should not try to give a complete performance for the camera (that is, control the representation on film) but must remember that the function of the actor is to give the director as much coverage as possible as a film, as well as a performance, is made in the editing room. According to Polley, this realization, that the film actor exists to serve the director, has given her new enthusiasm for acting. Thus, her career, and her career choices, can be seen as a quest for knowledge about the art of cinema, a journey whose fruition we will see in her future feature work as both actor and director.