Paul, an English former foreign exchange broker, and Nuala, an Irish homemaker and photographer, move their daughters – Zoe, Mischa and Hania – to New York City from London. Despite living in the U.S. most of her life, Barton tells PEOPLE in 2005, "I consider myself British."
After being asked to write and perform her own monologue at summer camp, 8-year-old Barton crafts a piece about turtles, catching the attention of a talent scout, who alerts her parents to her ability as a performer.
Pulitzer Prize-winning playwright Tony Kushner casts 9-year-old Barton in his play Slavs! as a young Russian, opposite Oscar winner Marisa Tomei. In 2004, Barton tells PEOPLE that Kushner "is the reason I act for a living."
After appearing on Broadway, Barton makes her film debut as a socially awkward 10-year-old opposite Sam Rockwell in the 1997 drama Lawn Dogs. Two years later, the still little-known actress plays a memorably spooky ghost in The Sixth Sense, opposite Haley Joel Osment and Bruce Willis. She later takes on roles in Notting Hill and Lost and Delirious.
After meeting producer McG while guest-starring on his short-lived crime series Fastlane, Barton is cast as the popular and privileged Marissa Cooper for his new FOX series The OC. "She was our only choice for Marissa," McG tells PEOPLE. The teen drama, which costars Benjamin McKenzie, Adam Brody and Rachel Bilson, soon draws huge audiences, propelling Barton to stardom.
After modeling for Calvin Klein jean ads and becoming a regular in the fashion mags, Barton is declared "a triple threat: in entertainment, fashion and beauty" by Women's Wear Daily. Topping off her OC success, Barton signs a two-year deal with skincare line Neutrogena.
Barton meets oil heir Brandon Davis, whose billionaire family was the inspiration for the 1980s nighttime soap Dynasty. In April, Davis confirms that they're in a relationship. The couple is a fixture on the Hollywood nightclub scene and vacation together in Saint Tropez. However, after more than a year of dating, Barton and Davis call it quits.
Barton starts filming The OH in Ohio, a drama in which she plays a teen who seduces a teacher played by Paul Rudd. "If you're considered a 'pretty' girl, then you have a really hard time having people open up to find you roles, because they want to peg you as something," Barton tells Allure in 2005. "So I've chosen quite dark characters." The indie film grosses less than $500,000 at the box office.
Barton further secures her foothold in the fashion industry when she signs on as a spokeswoman for cool-again Keds. The star has been a fan of the sneakers since she was a kid. "They were blue with white laces," she says to PEOPLE of her first pair. "I've been wearing Keds a lot lately, because they're comfortable, sexy and they go with everything."
In a much-talked-about episode of The OC, Barton engages in a kiss with another woman, played by Olivia Wilde, who her character briefly dates. Viewer reaction? "Very Supportive," The OC creator Josh Schwartz tells PEOPLE.
BIOGRAPHY (top to bottom): Jade Albert; Joan Marcus; Buena Vista/Photofest; FOX; Frank Micelotta/Getty; Anthony Dixon/London Features; Gregory Pace/Filmmagic; FOX