Her acting credentials rose with the 1996 film Feeling Minnesota. In the romantic comedy, Diaz plays a woman in a love triangle with two brothers. Her nuanced portrayal won her critical acclaim.

Diaz then appeared in a string of pictures, including She's the One and Head Above Water.

In 1997 Diaz was cast in My Best Friend's Wedding. She played opposite Julia Roberts as a 20-year-old University of Chicago student from a wealthy family. The two compete with each other to win the heart of the same man. Roberts praised Diaz for her performing skills and easy-going character. The comedy won big at the box office.

Diaz continued her success a year later in There's Something About Mary, directed by the Farrelly Brothers Bobby and Peter. The low-budget film gained a robust box office return with 176 million in the US alone and 369 million worldwide. It was the 4th highest grossing movie of 1998 in North America.