DuVall was born in Los Angeles, California, the only child of Rosemary (née Hatch) and Stephen DuVall. Her parents divorced when she was 12. After her mother remarried, DuVall dropped out of high school and moved into her own apartment. She sought entertainment in movies and television programs, memorizing entire scenes. DuVall decided she wanted to be an actress, and returned to high school, this time the Los Angeles County High School of the Arts, while working to support herself. She is not related to actors Robert Duvallor Shelley Duvall, who share their surnames with her.

Prior to making her debut in Little Witches, she worked in a coffee shop. DuVall's breakthrough role was in Robert Rodriguez's The Faculty in 1998, alongside Elijah Woodand Josh Hartnett Roles in Girl Interrupted, The Astronaut's Wife, She's All That, But I'm a Cheerleader, Ghosts of Mars and Thirteen Conversations About One Thing followed. After appearing in The Laramie Project, Identity and the Oscar-nominated 21 Grams, DuVall starred on HBO's Emmy Award-winning Carnivàle, which ran from 2003-2005. During that time, she also starred in Helter Skelter (which earned her a Satellite Award nomination) and alongside Sarah Michelle Gellarin Sam Raimi's The Grudge. Recent projects have included Itty Bitty Titty Committee, David Fincher's Zodiac and a recurring role on NBC's hit series Heroes. She'll next appear alongside Anne Hathawayin Passengers. In addition, DuVall has directed a short film called It's Not Easy Being Green, starring Leisha Hailey Carla Gallo and herself.