Born in Denver, Colorado and raised in Laguna Beach, California, she attended Laguna Beach High School as a teenager. In 2004, Cavallari came to prominence after being cast in the reality television series Laguna Beach: The Real Orange County, which documented the lives of her and her friends.
After moving to Los Angeles to pursue an acting career in 2006, Cavallari appeared in several television series as minor characters. In 2009, she replaced former Laguna Beach cast member Lauren Conrad in her Spin-off series The Hills, which was revamped to chronicle the personal and professional lives of Cavallari, Heidi Montag, and Audrina Patridge.
In 2011, Cavallari became engaged to Chicago Bears quarterback Jay Cutler. She gave birth to son Camden Jack, the first child for both, the following year. Cavallari and Cutler married in 2013.
Cavallari was born in Denver, Colorado, the second of two children of Judith Spies (née Eifrig) and Dennis Cavallari. When her mother divorced her father, her older brother, Mike, moved with their father to Laguna Beach, California, while she moved with her mother to the village of Barrington, Illinois, a suburb an hour northwest of Chicago. She attended Barrington Station Middle School, and graduated on to Barrington High School. After difficulties adjusting to a new life with a stepfather and stepbrother, Cavallari moved to California to live with her father. There, Cavallari was enrolled at Santa Margarita Catholic High School for her sophomore year. After she attended a Driver's Education course through Laguna Beach High School, her father enrolled her in Laguna Beach High School.
Cavallari was in her junior year of high school when the first season of Laguna Beach: The Real Orange County 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 plot lines.
In May 2009, Cavallari confirmed that she would be joining the cast of the popular MTV reality series The Hills. She appeared in the mid-season finale that aired on May 31, 2009, and appeared as a regular in the remainder of the fifth season. She inked a deal with MTV to appear as a series regular throughout two more seasons of the series following the fifth. The sixth and final season aired summer 2010.
Cavallari was on the 13th season of Dancing with the Stars and partnered with two-time champion, Mark Ballas. Despite having high scores, Cavallari was the third to be eliminated, shocking the audience, judges, and fellow dancers alike. One of the judges, Len Goodman, commented that he expected to see Cavallari dancing in the final. The cumulative average of Cavallari's dances were higher than of contestants who had lasted twice as long as she did.
Cavallari at the MTV Video Music Awards in 2009. After her stint on Laguna Beach, Cavallari headed to Los Angeles and briefly attended the Loyola Marymount University. She signed on the UPN reality television series Get This Party Started, which premiered February 7, 2006. The series was canceled after airing two episodes due to extremely low ratings. She guest starred on one episode of another UPN series, Veronica Mars. She has appeared in numerous television roles such as CSI: NY, Cane and Adventures in Hollyhood. In 2006, she signed on as Crystal in the horror film Fingerprints. She also played a small role in Wristcutters: A Love Story, an independent film, directed by Goran Dukic in 2006. In 2008, she had a supporting role as Summer in Spring Breakdown alongside Amy Poehler. The film was released straight-to-DVD on June 2, 2009, and received mixed reviews. She also starred in the independent film Green Flash alongside Torrey DeVitto. In 2009 she starred in the independent American high school comedy film, Wild Cherry, as Trish, which also starred Rumer Willis. She also starred in the straight-to-DVD film, National Lampoon's Van Wilder: Freshman Year, as Kaitlyn. The film was released July 14, 2009, to mixed to negative reviews.