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