She became famous during the 1990s with roles in the movies The Mask, My Best Friend's Wedding, and There's Something About Mary. Other notable movie credits include Charlie's Angels, and voicing the character Princess Fiona for the Shrek series. Diaz received Golden Globe award nominations for her performances in the movies There's Something About Mary, Being John Malkovich, Vanilla Sky, and Gangs of New York.
At age 16, she began her career as a fashion model. Diaz contracted with modeling agency Elite Model Management. For the next few years she worked around the world for contracts with major companies. She modeled for designers such as Calvin Klein and Levi's. When she was seventeen years old she was featured on the front cover of the July 1990 issue of the magazine Seventeen.
At age 21, Diaz auditioned for the movie The Mask, even though she had no previous acting experience, based on the recommendation of an agent for Elite who met the film's producers while they were searching for the female main actress. After obtaining the main female role, she immediately started acting lessons. The Mask became one of the top ten highest grossing films of 1994, and earned Diaz nominations for several awards.
Diaz received "substantial" defamation damages from suing American Media Incorporated, after The National Enquirer had claimed she was cheating on then-paramour Timberlake.
During 1992, Diaz featured in a soft-core sadomasochism video entitled "She's No Angel" filmed by photographer John Rutter. During 2003, she won an injunction against Rutter preventing him from distributing the video or accompanying photographs, but during 2004, the video was distributed online by a Russian internet website.
During 1995, she began a relationship with actor Matt Dillon, with whom she co-starred in There's Something About Mary; the relationship ended during 1998. She then had a relationship with singer/actor Jared Leto from 1999 to 2003. Diaz dated singer Justin Timberlake from 2003 to 2006.
During October 2004, Diaz and Timberlake were in an altercation with a tabloid photographer outside a hotel. When the photographer and another man tried to photograph them, the couple snatched the camera. Pictures of the incident appeared in Us Weekly. Representatives for the pair claimed that they were acting a scene on a set.
As of July 2010, Diaz has been in a romantic relationship with New York Yankees baseball star Alex Rodriguez.