After moving to Los Angeles to pursue an acting career in 2006, Cavallari appeared in several television series as minor characters.
Cavallari is married to Miami Dolphins quarterback Jay Cutler.
Cavallari was born in Denver, Colorado, one of two children of Judith Eifrig and Dennis Cavallari. She is of German and Italian descent.
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 she would be joining the cast of Laguna Beach's spin-off series, The Hills. She made her first appearance on the series during the fifth season's mid-season finale on May 31, 2009, at Heidi Montag and Spencer Pratt's wedding, where she caught the bouquet. The second half of the season premiered on September 29, 2009, with Cavallari assuming the position of former main cast member and narrator Conrad. Despite originally signing a deal with MTV to appear in two additional seasons following the fifth, the sixth and final season concluded on July 13, 2010.
Cavallari was on the 13th season of ABC's Dancing with the Stars and partnered with two-time champion, Mark Ballas. She was the third to be eliminated.
After Laguna Beach, Cavallari headed to Los Angeles and signed on the UPN reality television series Get This Party Started, which premiered February 7, 2006. The series was canceled after airing two episodes. She appeared on one episode of another UPN series, Veronica Mars, and went on to guest roles on series including CSI: NY, Cane, and Adventures in Hollyhood. In 2006, she signed on as Crystal in the horror film Fingerprints.
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.
Cavallari 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 Ellis Island. In February 2009, she posed for the NOH8 Campaign in support of gay marriage.
In January 2010, she traveled to El Salvador to do charity work. In March 2011, Cavallari traveled to Kenya to do charity work with the non-profit organization One Kid One World.
In March 2014, Cavallari drew national criticism for refusing to vaccinate her children, a decision she and her husband, Jay Cutler based on fears of a connection between childhood vaccination and autism.
From 2015-2016, the former website Gawker ran a series of daily articles on Cavallari for a streak of 415 days. The series, by Allie Jones, was called "500 Days of Kristin"—although it ended after just 415 days, with the publication of Cavallari's book Balancing in Heels. By treating Cavallari's quotidian Instagram posts as newsworthy, the series appeared to gently mock the culture of celebrity women on social media.
Cavallari began dating then Chicago Bears quarterback Jay Cutler in late 2010, and became engaged to him in April 2011. They called off the engagement in July 2011, but reconciled in November 2011. Cavallari and Cutler wed on June 8, 2013, in Nashville, Tennessee. They have three children: sons Camden (born August 8, 2012), Jaxon (born May 7, 2014) and daughter Saylor (born November 23, 2015).
Her brother, Michael Cavallari, was found dead on December 10, 2015, having died of hypothermia following a car crash.