Reid began acting at age six, becoming a regular on the game show Child's Play, and appeared in over 100 commercials for corporations including Jell-O, McDonald's, Crayola and Milton Bradley. As a teenager, she was on Saved by the Bell: The New Class.
After moving to Hollywood in 1997, Reid transitioned to movies, landing her breakout role in the cult-classic The Big Lebowski. Later that same year she appeared in Cruel Intentions and Urban Legend. Reid found her first taste of real mainstream success when she portrayed the role of the virginal Vickie in American Pie. The film marked her first to reach #1 at the box office. She reprised the role in American Pie 2, and in the fourth theatrical film in the series, American Reunion. Following the success of American Pie 2, Reid starred in a number of commercial and critical misfires including Josie and the Pussycats and Van Wilder. She also starred as the youngest daughter of a Texas gynecologist in Robert Altman's Dr. T & the Women, alongside Richard Gere. She returned to the small screen as a recurring character on the NBC sitcom, Scrubs, appearing in 11 episodes of season three. Shortly thereafter, Reid appeared alongside Ashton Kutcher in My Boss's Daughter, for which she was nominated for both Worst Supporting Actress and Worst Screen Couple at the 2004 Golden Raspberry Awards.
In 2005, she co-starred in infamous German filmmaker Uwe Boll's Alone in the Dark with Christian Slater. Her mispronunciation of "Newfoundland" became a popular internet catchphrase. The film was panned by critics and Reid received a Razzie Award nomination for Worst Actress. Reid signed on to host E!'s Taradise, a program that showcased high-society vacations and hot spots. The show premiered on August 10, 2005, but it was canceled in September, with Ted Harbert, E! Network's president, saying it was "incredibly difficult to produce with someone well-known." In January 2007, Reid filmed a commercial with Daniel Conn for Dodo, an Australian budget telephone and Internet service provider. Between 2007 and 2008, she starred in a number of direct-to-video films, including 7-10 Split/Strike, If I Had Known I Was a Genius (which was released at the 2007 Sundance Film Festival), and Clean Break/Unnatural Causes. She also played the main character in the made-for-television horror film Vipers. In 2010, she landed the role of Bonnie in the thriller film The Fields, which was released in 2011. In March 2011, she filmed a Funny or Die spoof trailer for The Big Lebowski 2.
On August 18, 2011, Reid was the second housemate to enter the British reality series Celebrity Big Brother 8. In September 2011, Reid announced via her official Twitter page that she was to appear in Jedward's new music video for "Wow Oh Wow", which they started shooting in late October of the same year. In 2014, she appeared in their music video for "Ferocious".
Recent and upcoming projects include comedy spoof The Hungover Games, horror film Charlie's Farm, the Bollywood-film Tie the Knot and the TV series The Big Big Show with Andrew Dice Clay, and Tom Green.