At 16 she began her career as a fashion model. Diaz signed with top modeling agency Elite Model Management. After graduating from high school, she went to work in Japan and met video director Carlo de la Torre. On her return to America, she moved in with him. For the next few years, her modeling took her around the world, working for contracts with major companies. She modelled for designers such as Calvin Klein and Levi's. She also graced the cover of the July 1990 issue of Seventeen magazine.

At 21, Diaz auditioned for The Mask. Even though she had no previous acting experience,after obtaining the lead female role, she immediately started acting lessons. Over the next three years, she won roles in low-budget, independent films, such as The Last Supper, Feeling Minnesota, and She's the One. She then regained mainstream success with her roles in My Best Friend's Wedding and There's Something About Mary, a film for which she was nominated for a Golden Globe for in the category of Best Actress - Musical or Comedy. She won critical acclaim for her performance in Being John Malkovich, which earned her Best Supporting Actress nominations at the Golden Globes, the BAFTA Awards and the SAG Awards.

During the 1999-2000 period, Diaz starred in many films, such as Things You Can Tell Just by Looking at Her, A Life Less Ordinary, Any Given Sunday, and the hit adaptation of Charlie's Angels. In 2001, she won nominations for Best Supporting Actress at the Golden Globes, the SAG Awards and the AFI Awards for Vanilla Sky, and also voiced Princess Fiona in Shrek, for which she earned $10 million. In 2003, Diaz received another Golden Globe nomination for Martin Scorsese's epic Gangs of New York, and became the second actress (after Wedding costar Julia Roberts) to earn $20 million for a role, receiving the sum for Charlie's Angels: Full Throttle. After Full Throttle, Diaz only appeared in three films, Shrek 2, In Her Shoes and The Holiday . During 2004 and early 2005, Diaz explored some of the planet's environmentally unique locations while discovering ways to help preserve them for the 10-episode MTV series Trippin' which featured numerous celebrities and friends of Diaz, such as Jessica Alba, Drew Barrymore, Mark Hoppus, Eva Mendes and Justin Timberlake.

Diaz returned to the screen for Shrek the Third in 2007, where she co-stars with former boyfriend Justin Timberlake. She was set to team up again with The Mask co-star Jim Carrey in the film Fun with Dick and Jane, but dropped out to star in In Her Shoes. She will also appear in Shrek 4 and in the romantic comedy What Happens in Vegas, opposite Ashton Kutcher. She is also set to star in The Box, a horror thriller in 2008 co-starring James Marsden.