Amy was born in Topanga, California. Her mother, Judy Lysle, worked at a museum, and her father, John Boden Smart, was a salesman. Amy studied ballet for ten years.
While modelling in Italy, Amy met fellow model Ali Larter and the two became istant friends, according to Larter. In Los Angeles, the two took acting classes together. After appearing in the video for The Lemonheads It's About Time in 1993, Amy's first film role was in director Martin Kunert's film Campifre Tales, followed by a small role as Queenie in the 1996 rendition of John Updike's short story, A&P. She had a minor role in the 1997 film Starship Troopers as the co-pilot for Carmen Ibanez. She had a starring role in the mini-series The 70s, playing a young woman from Ohio. In 1999, Amy played the girlfriend of a popular football player in the film Varsity Blues, re-uniting her with Larter.Amy played a recurring character on the series Felicity from 1999 to 2001. She co-starred in the films Road Trip, Rat Race, Starsky & Hutch, and The Butterfly Effect. In 2005, Amy co-starred with Ryan Reynolds in the romantic comedy film Just Friends, which had a total domestic box office gross of $32,619,761, and a total worldwide box office of $50,871,598. In 2003 Amy also had a small role in the American sitcom Scrubs, playing Jamie Moyer, one of main character J.D.'s love interests.
In 2005, Amy starred as Sarah in the British indie-film called The Best Man. Seth Green was her c-star. She also appeared in the 2006 film Crank, portraying the girlfriend of the lead character, Chev Chelios. She reprised the role in the sequel, Crank: High Voltage, released in 2009. Amy was a regular cast member in the short-lived 2006 CBS television series Smith. She also voiced some of the characters in the animated series Robot Chicken, created by Seth Green. Amy appeared as Joy in the 2006 film Peaceful Warrior, starring Scott Mechlowicz and Nick Nolte. She stars as Melissa in the 2008 indie-film Seven Moon. In 2011, Amy joined the Showtime dramedy Shameless as the recurring character Jasmine Hollander.