Catherine Ann Bosworth was born on January 2, 1983 in Los Angeles, California as the only child of Hal Bosworth, an executive for Talbots, and Patricia Potter, a homemaker. She was born with sectoral heterochromia, resulting in a hazel section at the bottom of her right blue eye, while the left is completely blue. After leaving San Francisco at the age of six, Bosworth's family frequently moved around the country because of her father's job, and she grew up mainly on the East Coast, spending the rest of her youth in Darien, Connecticut and Cohasset, Massachusetts. She has noted that because of her family's frequent relocations, she always felt like the "new girl in school", and describes herself as "shy" and unpopular during her high school years, saying that she has "this pain in [her] heart from what it was like to walk in with your lunch tray and not have anywhere to sit".
While attending Cohasset High School (which she graduated from in 2001), Bosworth learned to speak Spanish and was a member of the National Honor Society; she also played varsity soccer and lacrosse. Bosworth has always been interested in a professional career as a competitive horse racer and, by the age of fourteen, she was a champion equestrian.
Bosworth's first film role came after an open casting call in New York for the supporting part of Judith in the 1998 film, The Horse Whisperer. The film's producers needed someone who was already an experienced horse rider, leading to Bosworth's successful audition for the role. She subsequently had a small part in the 2000 film Remember the Titans. In 2001, Bosworth moved to Los Angeles in hopes of obtaining easier access to auditions and better film parts. Her first leading role was in 2002's surfing movie Blue Crush, which she prepared for by working out with two separate trainers six hours a day for months in order to add fifteen pounds of muscle to her frame. The film received positive reviews and grossed $40 million at the United States box office, allowing Bosworth wider exposure to a mainstream audience.
Between 2002 and 2005, Bosworth appeared in a number of widely released films. She starred as actress Sandra Dee in Beyond the Sea and played the lead role in Win a Date with Tad Hamilton!, opposite Topher Grace. Bosworth also portrayed Chali, a Hare Krishna, in a film adaptation of Myla Goldberg's acclaimed novel Bee Season, about a dysfunctional Jewish family. She has appeared in several Revlon ads and ranked as #60 in FHM's "100 Sexiest Women in the World 2005" list. For two years running, she has placed on the Maxim Hot 100 List – #38 in 2005 and #8 in 2006.
After going through many screen tests and competing with other actresses for the role, she was cast as reporter Lois Lane in the highly anticipated adaptation to the Superman comics, Superman Returns. She starred along with her Beyond The Sea co-star Kevin Spacey, as well as newcomer Brandon Routh as Superman. A sequel to Superman Returns is planned for a release in the summer of 2009.
Bosworth will star in a psychological drama called The Girl In The Park with Sigourney Weaver and Keri Russell. She plays Louise, who is assumed to be the missing daughter of Weaver's character. This movie is written and directed by Pulitzer Prize winner David Auburn in his directorial debut. Filming began in November 2006 and will be completed by early January. It is expected for release towards the end of 2007 to possibly an early 2008 release.
Bosworth was accepted to Princeton University in late 2000, but continues to defer her attendance. She is also a member of the Appalachia Service Project.
Bosworth previously dated actor Matt Czuchry, whom she met on the set of their short-lived television series, Young Americans. Their relationship lasted from 2000 to 2002. Then, in late 2002, she began dating actor Orlando Bloom. The two met outside a coffee shop and were introduced to each other by a friend, before meeting again at the premiere of The Lord of the Rings: The Two Towers. Bosworth and Bloom separated in 2005 but shortly after resumed their relationship. On September 5, 2006, Entertainment Tonight reported that her on-again, off-again relationship with Bloom had ended after almost four years though it is unclear when the split took place Bosworth has been dating British model James Rousseau since September 2006.
In mid to late 2006, Bosworth made headlines with her extremely thin appearance. She has become part of a trend of young Hollywood actresses who have debuted new, alarmingly thin bodies.
Bosworth has two cats, Louise and Dusty, and a dog named Lila, whom she adopted while on a 2004 vacation in Morocco. She has noted that although equestrianism is her hobby, she has been unable to practice it, because of the potential risk of injury involved affecting her film career.