Conrad was born in Laguna Beach, California on February 1, 1986 to Jim, an Architect, and Kathy (née Lawrence). She has two younger siblings, a sister named Breanna, also a television personality, and a brother, Brandon. Conrad first expressed an interest in a career in the fashion industry when she was in the sixth grade. Her father added that Conrad "wasn't a great student [and] wasn't that interested" during her childhood, although noted that "we figured out along the way that she was an Artist and her real love was fashion."

Since appearing on Laguna Beach: The Real Orange County, Conrad has been recognized as being among the first individuals to benefit from the popularity of reality television in the early 2000s. In 2009, Thomas Rogers from Salon described her as "one of the dullest major characters in reality television history", but opined that her normalcy compared to her co-stars on The Hills made her "vaguely likable". An Editor from People stated that Conrad "became a full-blown TV phenom" during its third season, which notably introduced the conflict with Montag and Pratt, in addition to controversy regarding scripting allegations.

After graduating from high school in 2004, Conrad attended the Academy of Art University in San Francisco for one semester, where she met Heidi Montag. Conrad left the series after the second season, during which period she moved back home and transferred to the Fashion Institute of Design & Merchandising in Los Angeles. After her sister Breanna became a primary cast member, Conrad made a guest appearance on the series during the third season in 2006.

After moving to Los Angeles in May 2006, the spin-off series The Hills was developed to chronicle the lives of Conrad, her housemate Montag, and their friends Audrina Patridge and Whitney Port. During production of the first season, Conrad and Port held internships with Teen Vogue under the direction of West Coast Vogue Editor Lisa Love; she stated that they had to interview successfully for the positions, "regardless of what the cameras wanted". By the second season, their friendship had deteriorated after Montag began dating Spencer Pratt. After Montag moved in with Pratt, Patridge and Lo Bosworth later became roommates with Conrad.

During the third season, Conrad ended her friendship with Montag after she suspected that Montag and Pratt were responsible for rumors of a sex tape involving herself and her former boyfriend Jason Wahler; the ensuing feud carried through each subsequent season in which Conrad appeared. Conrad briefly dated fellow castmate Brody Jenner, which she commented had been subject to "editing to drag it out" during the series. In January 2007, Conrad was announced as the inaugural spokeswoman of Avon Products's "mark." line, marketed towards young women; she was succeeded by Actress Ashley Greene in June 2010. Later in 2007, Conrad appeared as a satirical version of herself in the comedy film Epic Movie. In 2008, Conrad and Port began employment with Kelly Cutrone's PR firm, People's Revolution. Conrad later made a cameo appearance in an episode of Greek and provided her voice for a cartoon version of herself in an episode of Family Guy. In March, she premiered her first fashion line The Lauren Conrad Collection. After underwhelming sales figures, Conrad ended the line the following year to further familiarize herself with the industry.

During its production, Conrad was the highest-paid cast member on The Hills, earning an annual salary of $2.5 million. In 2008, her endeavors earned her an additional $1.5 million. In 2010, Conrad was named the second highest-paid reality television personality, ranking behind Kim Kardashian. Conrad is a registered member of the Republican Party. She has stated that she has "done several things to [...] encourage people to vote", but respects the private ballot and "[doesn't] want to ever influence someone's vote or have [her] vote change someone's opinion of [her]". Conrad collaborated with Seventeen magazine to film a public Service announcement for Declare Yourself, a campaign which encouraged young adults to register themselves to vote during the 2008 presidential election. She has additionally expressed her support for same-sex marriage, and on one occasion left a Mexican restaurant after learning of its disapproval of marriage equality.

Conrad's first novel L.A. Candy was released in June 2009, and became a bestseller on The New York Times. It was inspired by her life, focusing on a woman named Jane Roberts who moves to Los Angeles. It was followed by sequels Sweet Little Lies and Sugar and Spice in 2010. Conrad also released the fashion guide Lauren Conrad Style in 2010. She later made appearances on the syndicated game show Who Wants to Be a Millionaire, playing for her charity "m.powerment by mark" and Kathy Griffin: My Life on the D-List, and also served as a guest judge on the thirteenth cycle of America's Next Top Model. In fall 2009, Conrad collaborated with Kohl's to launch her second fashion line LC Lauren Conrad, and was later expanded to include a bedding collection.

In September 2010, Conrad revealed that she had filmed an alternate ending for The Hills with Jenner. Upon the conclusion of their month-long morning marathon of the series, titled "RetroMTV Brunch", MTV aired the footage in August 2013. The scene depicts Jenner returning to his apartment after seeing Cavallari's limousine off to Europe. Conrad is revealed to be sitting on his couch, and comforts him that "it's hard to say goodbye" to a "friend of [his]", before the camera focuses on a smiling Conrad. That month, she also expressed interest in participating in a potential reunion film. In December 2013, Montag stated that she and Conrad have "talked a few times" since the series' conclusion, elaborating that "it's unfortunate things happened the way that it did, but we're both different people now, older and more mature."

Conrad has been featured on the covers of several magazine's best-selling issues, including those of People StyleWatch and Cosmopolitan. She appeared on the May 2012 issue of Glamour, which sold approximately 500,000 copies and became the magazine's strongest-selling issue of the year, and was featured on the covers of the second highest-selling issues of Lucky and Marie Claire in 2013. Lauren Sherman from Fashionista credited Conrad's success to "her knack for entrepreneurship, her easy style, and her friendliness". Jim Higgins from Milwaukee Journal Sentinel complimented her pursuit of several different career endeavors, and compared her to a "young Martha Stewart". However, in August 2012, Conrad was criticized for destroying a collection of A Series of Unfortunate Events novels for a crafting tutorial posted to YouTube.

In 2013, Misty White Sidell from The Daily Beast noted that Conrad established a following based on her respectability instead of "bitch-slaps and drunken sex-capades", further commenting that her more relatable image made her an "anomaly" among television personalities. Conrad herself commented that The Hills was intended to be an "aspirational" program despite being "laced with scandal and catfights", stating that the storyline differed from the "shock value" emphasized in recent programming. Conrad has additionally been recognized for originating several now-famous quotes on The Hills, including "He's a sucky person!" when criticizing Spencer Pratt during the second season, and "You know what you did!" when arguing with Heidi Montag over her alleged involvement with sex tape rumors involving herself in the third season.

Having begun dating in February 2012, Conrad and law student and former Something Corporate Guitarist william Tell, moved into a shared residence in Westwood, Los Angeles in September 2013, and announced their engagement the following month. That October, Conrad and her friend Hannah Skvarla opened the online store The Little Market, which distributes handmade pieces from women of varying cultural backgrounds. Conrad and Tell got married on September 13, 2014 in California. On January 1, 2017, Conrad announced via instagram that she and Tell were expecting their first child. Their son, william "Liam" James Tell, was born on July 5, 2017.

Conrad released limited-run Cinderella, Minnie Mouse, and Bambi-inspired collections for LC Lauren Conrad in February, May, and October 2015, respectively. She also introduced an upscale runway collection for the line during New York Fashion Week that September.

In 2017, Conrad launched an affordable swim line at Kohl's to expand her brand.