Kristin Cavallari was born in Denver, Colorado, the younger of two children. When her parents divorced, her older brother moved with their father to Laguna Beach, California, while she moved with their mother to Barrington, Illinois, a suburb northwest of Chicago. After having trouble adjusting to a new life with a stepfather and stepbrother, Cavallari moved to California to be with her dad and brother, and was enrolled at Santa Margarita Catholic High School her freshman year of high school. After attending a Driver's Education course through Laguna Beach High School, her father enrolled her in LBHS.

Cavallari was in her junior year of high school when the first season of Laguna Beach began production. At the time, she was involved in an on-and-off relationship with senior Stephen Colletti. Cavallari's romance with Colletti caused a rivalry with another cast member, Lauren Conrad. The love triangle became one of the series' central plotlines.

After her stint on Laguna Beach, Cavallari headed to L.A. and briefly enrolled at Loyola Marymount University. She then landed a hosting gig on UPN's Get This Party Started. The series drew low ratings and was canceled after only two episodes. Cavallari continued to pursue a career in acting, landing a guest role on Veronica Mars, and a lead role in Teddy Geiger's music video, "For You I Will (Confidence)". She has also starred in the new Gavin Degraw video for the song "I'm In Love With A Girl".

In September 2007, Cavallari began shooting the film, Green Flash. She also has roles in two upcoming films; Fingerprints and Spring Breakdown, both set for release in 2008.

In addition to film and tv work, Cavallari has also modeled. She was featured in ads for Bongo jeans, and has appeared in Seventeen, Teen People, Teen Vogue, Rolling Stone, Blender and GQ. In 2006, Maxim named her #23 on its annual Hot 100 List, and was also featured as part of its "Hottest Women of Reality TV" later that year.

She has been involved in the "Until There's a Cure" public service advertising campaign to raise awareness and funds for AIDS and HIV research and vaccine development. In 2006, Cavallari appeared in ads for PETA, and has also appeared as a celebrity spokesperson for "We Are Ellis Island", a campaign for the restoration of historic buildings on Ellis Island.

During the filming of Laguna Beach, Cavallari dated fellow cast member Stephen Colletti. After the end of her relationship with Colletti in 2004, Cavallari began dating Brody Jenner, son of Olympic decathlon champion Bruce Jenner. The couple broke up in 2006.

Cavallari has also been romantically linked to Nick Lachey, New York Islanders forward Mike Comrie, and Arizona Cardinals quarterback Matt Leinart.

Cavallari dated actor Nick Zano from 2006 until December of 2007. She has been seen with Matt Leinert early this year.