Upon the conclusion of the fourth season of The Hills in December 2008, Conrad wished to leave the series to pursue other career opportunities. However, per the producers' requests, she filmed ten episodes for the following season, in which she closed her storylines. Conrad made her final appearance on the series in May 2009, attending Montag and Pratt's wedding after much deliberation during the mid-season finale of the fifth season. However, in the July 2009 issue of Cosmopolitan, she stated that producers had pressured her into a reconciliation with Montag throughout the season, adding that she was displeased when they would not allow otherwise. Conrad was replaced by former Laguna Beach castmate Kristin Cavallari until the series' conclusion in July 2010.
In March 2008, 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.
Conrad made a cameo appearance in an episode of Greek in 2008 and provided her voice for a cartoon version of herself in an episode of Family Guy in 2009. 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.
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. Despite having been reported to be a registered member of the Republican Party, Conrad has stated that she has "done several things to ... encourage people to vote", and 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.
In 2008, Conrad began dating actor Kyle Howard. Howard expressed concern that appearing on reality television would interfere with his acting career; consequently, their relationship was not documented on The Hills. (After three years together, Conrad and Howard ended their relationship in 2011.)