Cuthbert was born in Calgary, Alberta, daughter of Patricia, a homemaker, and Kevin, an automotive design engineer. She has two younger siblings, Jonathan and Lee-Ann. She grew up in Greenfield Park, near Montreal, Quebec. She also lived for some time in Toronto, Ontario before moving onto acting. In 2000, she graduated from Centennial Regional High School and moved to Los Angeles at 17 to act.
When she was 9, Cuthbert started modeling 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. 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.
2002–2005: Commercial success
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."