When she was 9, Cuthbert started modelling children's clothing and also became a foot model. She made her first televised appearance as an extra in the horror-themed series for children, Are You Afraid of the Dark?; she later became a regular on the show. Cuthbert co-hosted Popular Mechanics for Kids with Jay Baruchel, filmed in Montreal. Her reporting captured the attention of Hillary Clinton, who invited her to the White House.
Cuthbert landed her first role in a feature film in the family drama Dancing on the Moon (1997). She appeared in other Canadian family movies and in an airplane thriller, Airspeed. Cuthbert co-starred in Believe a Canadian movie with Ricky Mabe in 2000. She starred in the Canadian television movie, Lucky Girl, in 2001 and was awarded a Gemini Award for her performance.
Soon after her move to Hollywood, she was cast as Kim Bauer, daughter of federal agent Jack Bauer, in the television series 24. She appeared in the show's first three seasons, but not in its fourth; she guest-starred in two episodes in the fifth season. She also reprised her role as Kim Bauer in 24: The Game and again guest-starred in five episodes
of the seventh season and in two episodes of the eighth season.
She began her Hollywood film career with small roles in Old School and Love Actually in 2003.
Cuthbert's next film, The Girl Next Door, was her first lead role. She played an ex–porn star, Danielle, opposite Emile Hirsch. She had reservations about the part, but was persuaded by director Luke Greenfield. She researched the role, speaking to adult actresses from Wicked Pictures and Vivid Entertainment. The film was compared to Risky Business, – although Cuthbert said her character was not directly based on Rebecca De Mornay's. Critics were divided; some praised the film for boldness, others, notably Roger Ebert, called it gimmicky and exploitative. Ebert wrote that he saw Cuthbert's character as "quite the most unpleasant character I have seen in some time."
In her next film, Cuthbert starred with Paris Hilton and Chad Michael Murray in the 2005 remake of the horror film House of Wax. Cuthbert, with the rest of the cast, was made up to look haggard. In one scene, her character was to attempt to open her mouth while her lips were sealed with glue. For realism, she used Superglue over prosthetics. House of Wax was largely panned, critics citing a range of flaws. It was called "notable for having some of the most moronic protagonists ever to populate a horror film," though of those characters, critics tended to think Cuthbert "fares the best." Though receiving negative reviews the film was a box office success. Others noted Cuthbert as an "exception," playing her role "earnestly" and "fine."
At the 24 season finale in May 2009.
Cuthbert's next film was the indie film The Quiet. She was co-star and co-producer. She played Nina, a temperamental 17-year-old cheerleader who suffers sexual abuse by her father. Cuthbert looked to her younger cousin as inspiration for how to play a teenager. The Quiet, distributed by Sony Pictures Classics, premiered at the 2005 Toronto International Film Festival and received a limited release in Los Angeles and New York City on August 25, 2006, before expanding regionally in the USA on September 1.
Cuthbert appeared in the music video for Weezer's "Perfect Situation" in early 2006, playing the group's fictional original singer who threw a tantrum that led to Rivers Cuomo, the roadie, becoming frontman of the band. She also had a small role in Paris Hilton's music video for the song "Nothing In This World".
In 2007, Cuthbert appeared in Captivity, a thriller centered on a fashion model taunted by a psychopath who has imprisoned her in a cellar, a role for which she was nominated for a Razzie award as "worst actress."
In He Was a Quiet Man, Cuthbert played Vanessa, a quadriplegic, starring with Christian Slater. The film was in limited release in 2007, and it was released on DVD in early 2008.
In 2008, Cuthbert appeared in My Sassy Girl, a remake of a Korean film, starring with Jesse Bradford. Her next film was the family comedy, The Six Wives of Henry Lefay, with Tim Allen, in which she played his daughter. She starred in the Canadian miniseries Guns. She was a judge in season two, episode two of Project Runway Canada, in which designers were challenged to create a "party dress" for her.
Cuthbert reprised her character Kim Bauer in the seventh season of 24 for five episodes. She was also to star in the CBS drama pilot Ny-Lon, playing a New York literacy teacher/record-store clerk who embarks on a transatlantic romance with a London stockbroker. The project, based on a British series starring Rashida Jones and Stephen Moyer, was canceled.
In December 2009, ABC said Cuthbert had joined the cast of The Forgotten in a recurring role as Maxine Denver, a Chicago professional.
From April 2011 to May 2013, Cuthbert starred as Alex Kerkovich for three seasons on the ABC ensemble comedy Happy Endings alongside Eliza Coupe, Zachary Knighton, Adam Pally, Damon Wayans Jr. and Casey Wilson. Despite critical acclaim and having a cult following, the show was cancelled by ABC after the conclusion of its third season on May 3, 2013.
In October 2012, she appeared in The Gaslight Anthem's music video "Here Comes My Man," playing the girlfriend of a man who mistreats her, until she imagines a romantic relationship with a character in a movie and chooses to end her real relationship.
In February 2014, Cuthbert signed on to play the female lead in Liz Feldman and Ellen DeGeneres' new NBC sitcom pilot One Big Happy. Cuthbert stars as Lizzy, a lesbian who gets pregnant just as her straight male best friend Luke (played by Nick Zano) meets and marries the love of his life, Prudence. The pilot was ordered to series on May 9, 2014 and will debut mid-season in early 2015.
In the media
In the past, Cuthbert regularly secured a place in FHM and Maxim's annual "hottest women" lists. Her highest ranking was No. 4 in the 2008 UK Edition of FHM's 100 Sexiest Women in the World list. She was ranked No. 14 in 2003, No. 10 in 2004, No. 5 in 2005, No. 22 in 2006, No. 10 in 2007 and No. 7 in 2009. The U.S. Edition ranked her No. 53 in 2003, No. 63 in 2004, and No. 54 in 2006. She was not listed in the U.S. 2005 list. Cuthbert was ranked No. 10 by AskMen.com readers in the list "Top 99 Women of 2007." In Maxim's Hot 100 list, she was ranked No. 84 in 2002, No. 9 in 2003, No. 21 in 2004, No. 92 in 2006, No. 25 in 2007, No. 6 in 2008, No. 43 in 2009, No. 65 in 2011, No. 34 in 2012, and No. 10 in 2013. The magazine also featured her in its Girls of Maxim Gallery. BuddyTV ranked her No. 33 on its TV's 100 Sexiest Women of 2011 list.
Cuthbert has two younger siblings, Jonathan and Lee-Ann. She is an avid ice hockey fan; in 2005, she maintained a blog on the NHL's website, though she did not post for most of the season.
Cuthbert dated NHL player Sean Avery for nearly two years; they broke up in August 2007. Cuthbert began dating NHL player Dion Phaneuf in May 2008. She was the subject of media attention over these relationships in December 2008, when Avery told reporters that "it's become like a common thing in the NHL for guys to fall in love with my sloppy seconds". He was subsequently suspended for the comment.
Cuthbert and Phaneuf announced their engagement in September 2012, and they married on July 6, 2013 at St. James Catholic Church in Summerfield, Prince Edward Island. Living in Toronto during the hockey season, Cuthbert and Phaneuf spend their summers at Phaneuf's waterfront estate outside of New London, Prince Edward Island, in his parents' home province.
Cuthbert's favourite hockey team is the Toronto Maple Leafs which her husband Dion Phaneuf captains. She has been known to attend games and sport Leafs merchandise.