A native of Los Angeles, Smart began her career modeling in Italy and subsequently enrolled in acting school. Her first role in film was in director Martin Kunert's anthology horror film Campfire Tales, followed by a minor part in Paul Verhoeven's Starship Troopers (1997). She garnered widespread recognition after appearing in the mainstream teen drama Varsity Blues (1999), as well as for her recurring role as Ruby on the television series Felicity (1999–2001). She followed this with a lead in the college sex comedy Road Trip (2000), and co-starred in Jerry Zucker's ensemble comedy Rat Race (2001). She had a lead role opposite Ashton Kutcher in the sci-fi drama The Butterfly Effect (2004).