Paré was born in Montreal, Quebec, Canada, the daughter of Anthony Paré, the head of the education department at McGill University, and Louise Mercier, a conference interpreter. She grew up in the Montreal neighbourhood of Notre-Dame-de-Grâce and has three brothers. Paré is bilingual, speaking both English and French. Her family is Catholic.
Paré's parents were both actors; her father was a drama teacher and toured with a theatre company. Her mother acted in amateur productions. Paré would watch her father at rehearsals as a child, and became interested in acting herself when helping him learn his lines for The Tempest. She attended Villa Maria, a private Catholic girl's high school in Montreal. Paré studied drama at TheatreWorks[disambiguation needed], and appeared in over half a dozen amateur theatre productions as a teenager, including a role as Maid Marian in Robin Hood.
Paré landed a small role in Bonanno: A Godfather's Story, a mafia TV movie, during her final year in high school, which convinced her to pursue acting as a career. She also found small roles in an episode of the horror/teen TV series Big Wolf on Campus and in the French film En Vacances in 1999. She dropped out of the fine-arts program at Montreal's Dawson College and pursued acting for two years. At one point, she worked as a photographer's assistant on automotive photo shoots.
After auditioning for a bit part for the independent film Stardom (2000), director Denys Arcand chose Paré to star in the film. She played a naive ice hockey player propelled to international stardom as a supermodel, co-starring with Dan Aykroyd. The comedic satire closed the 2000 Cannes Film Festival with mixed reviews from critics. Paré became the Canadian film industry’s "it girl" following the release of the film. She was voted one of the 25 most beautiful people in Canada by a Canadian magazine, but she did not take the title very seriously.
Paré next starred in Lost and Delirious (2001), opposite Piper Perabo, in a story of two young lovers set in a girls' boarding school. The film was the English-language debut of director Léa Pool, and debuted to positive reviews at the Sundance Film Festival. Paré appeared in the miniseries Random Passage in 2002, based on a series of award-winning novels by Bernice Morgan, and set in Newfoundland in the 1800s. Also that year, she appeared in the miniseries Napoléon as the emperor’s mistress. She had a cameo as a pop singer in Deepa Mehta's Bollywood/Hollywood, and starred in the girl gang thriller Posers. Paré next appeared in the CTV miniseries The Death and Life of Nancy Eaton (2003), directed by Jerry Ciccoritti, in the title role of murdered heiress Nancy Eaton.
Paré made her Hollywood film debut in the 2004 feature Wicker Park, directed by Paul McGuigan, as Josh Hartnett's fiancee. Paré starred in Lives of the Saints that year, with Sophia Loren and Kris Kristofferson, a TV miniseries set in the 1960s. She was in the mockumentary See This Movie, with Seth Meyers and John Cho, and had a role on the teen drama series Jack & Bobby that year. The WB television series was about two brothers, one who grows up to be President of the United States; Paré's character, Courtney Benedict, grows up to be First Lady.
Paré shot the TV pilot Protect and Serve with Dean Cain in 2007. She filmed the independent French-Canadian romantic comedy Jusqu'à toi that year. Paré co-starred as Liza, along with Justin Bartha, Mélanie Laurent and Billy Boyd. She had a small role in The Trotsky, a comedy filmed in Montreal in late-2008, directed by Jacob Tierney. She also filmed Suck, beginning in November 2008, a vampire horror-comedy written and directed by Rob Stefaniuk.Paré learned to play the bass guitar for the role. Suck premiered at the 2009 Toronto International Film Festival as part of the Contemporary World Cinema programme. She was nominated for a 2010 Canadian Comedy Award for best female performance in film for the role.
Paré filmed Red Coat Justice by Wyeth Clarkson in 2009. She had a role in the 2010 comedy Hot Tub Time Machine, starring John Cusack, Craig Robinson, Rob Corddry and Clark Duke. Paré played a groupie from character Nick (Craig Robinson)'s past. Paré appears in the Canadian comedy Peepers, written and directed by Seth W. Owen, along with Joe Cobden, Paul Spence, and Ricky Mabe. The film, about pleasures in voyeurism, competed in the Just for Laughs film festival in Montreal in July 2010. She plays Megan Calvet, Don Draper's secretary, on the television series Mad Men.
Paré has lived in Los Angeles, California since 2004. She married American writer and producer Joe Smith in 2007, but the couple have separated. Paré has since been living in Santa Monica with two other actresses. Paré has commented that she has refused to risk losing close relationships over pursuing a career in film and has made her family life a priority.