Stewart was born and raised in Los Angeles, California, where she currently lives with her family. Her father, John Stewart, is a stage manager and television producer who has worked for Fox. Her mother, Jules Mann-Stewart, is a scriptwriter originally from Maroochydore, Queensland, Australia. She attended school until the seventh grade, and then continued her education by correspondence. She has an older brother, Cameron Stewart, and is a guitar player. A fan of rock music, her favorite bands include Van Morrison, Radiohead, U2, The Beatles, The Specials, Laura Marling, The Rolling Stones, Nirvana and Beck. In a 2008 interview with Vanity Fair, Kristen confirmed she is dating actor Michael Angarano. She is also very close friends with her Twilight co-stars Robert Pattinson and Nikki Reed. Stewart has expressed a desire to live and work in Australia, saying, "I want to go to Sydney University in Australia. My mom's from there." Apart from acting, she is also interested in attending college in the near future, saying, "I want to go to college for literature. I want to be a writer. I mean, I love what I do, but it's not all I want to do—be a professional liar for the rest of my life."
Stewart's acting career began at the age of eight, after an agent saw her perform in her elementary school's Christmas show. Stewart's first role was a short, nonspeaking part in the Disney Channel TV production The Thirteenth Year. She subsequently appeared in the independent film The Safety of Objects, in which she played the tomboy daughter of a troubled single mother (Patricia Clarkson). Stewart had a major role in the Hollywood film Panic Room, playing the sullen, diabetic daughter of a divorced mother (Jodie Foster). The film received generally positive reviews, and Stewart garnered positive notices for her performance.
After Panic Room's success, Stewart was cast in another thriller, Cold Creek Manor, playing the daughter of Dennis Quaid and Sharon Stone's characters; the film generally failed at the box office. Her first starring role followed, in the children's action-comedy Catch That Kid, opposite Max Thieriot and Corbin Bleu. Stewart also played the role of Lila in the thriller Undertow. To date, Stewart's most critically acclaimed role may be in the television film Speak (2004), based on the novel by Laurie Halse Anderson. Stewart, thirteen at the time of filming, played high school freshman Melinda Sordino, who stops almost all verbal contact after being raped and who deals with enormous amounts of emotional turmoil. Stewart received great praise for playing the character, who had only a few speaking lines, but kept up a dark-witted commentary inside her head throughout the film.
In 2005, Stewart appeared in the fantasy-adventure film Zathura, playing the role of Lisa – an irresponsible older sister of two little boys, who turn their house into a spacecraft hurtling uncontrollably in outer space by playing a board game. The movie received praise by critics, but Stewart's performance didn't garner much media attention as it was noted that her character is immobilized during most of the movie. The following year, she played the character Maya in Fierce People, directed by Griffin Dunne. After that film, she received the lead role of Jess Solomon in the supernatural thriller movie The Messengers.
In 2007, Stewart appeared as teenager Lucy Hardwicke in In the Land of Women, a romantic drama starring Meg Ryan and The O.C. star Adam Brody. The movie, as well as Stewart's performance, received mixed reviews. That same year, Stewart starred in Sean Penn's critically acclaimed adaptation film Into the Wild. For her portrayal of Tracy – a teenage singer who has a crush on young adventurer Christopher McCandless – Stewart received generally positive reviews. Salon.com considered her work a "sturdy, sensitive performance", and the Chicago Tribune noted that she did "vividly well with a sketch of a role." Meanwhile, Variety magazine's critic Dennis Harvey commented skeptically, "It's unclear whether Stewart means to be playing hippie-chick Tracy as vapid, or whether it just comes off that way." After Into the Wild, Stewart had a cameo appearance in Jumper and also appeared in What Just Happened, which was released in October 2008. She also co-stars in The Cake Eaters and The Yellow Handkerchief, both independent films that have only been screened at film festivals.
On November 16, 2007, Summit Entertainment announced that Stewart would play Isabella "Bella" Swan in the movie Twilight, based on Stephenie Meyer's bestselling vampire/human romance novel of the same name. Stewart was on the set of Adventureland when director Catherine Hardwicke visited her for an informal screen test which "captivated" the director. She stars alongside Robert Pattinson, who plays Edward Cullen, her character's vampire boyfriend. The film began production in February 2008 and finished filming in May 2008. Twilight was released domestically on November 21, 2008. Stewart will be reprising her role as Bella in the sequel, New Moon, in 2009.
During a radio interview with Big O and Dukes of WJFK 1067, Jason Mewes stated that he is doing a movie called K-11 with Stewart and Nikki Reed, also of Twilight. The film, which is being directed by Stewart's mother, takes place in a dorm of the Los Angeles County Jail, and will feature both Stewart and Reed as male characters. Stewart was also cast to portray Joan Jett in The Runaways, a rock 'n' roll biopic of the titular band from writer-director Floria Sigismondi.