Mendes was raised in Los Angeles by her mother after her parents' divorce during her early years. Her father was a car salesman and her mother, also named Eva, is now an elementary school principal. She has two sisters and a brother. She was raised Roman Catholic and aspired to be a nun. As a child, Mendes was teased about her "buck teeth".
As a child she lived in Miami, Florida, and Los Angeles, California. She attended Hoover High School in Glendale and later attended California State University, Northridge to study marketing, but dropped out after meeting boyfriend Zedrick Threatt, who helped her to begin an acting career. She studied with Ivana Chubbuck.
One day she caught the eye of an agent who convinced her to pursue acting more steadily. Mendes worked her way up through commercials to music videos to guest roles in soap operas and supporting film roles. Her first film appearance was in the direct-to-video Children of the Corn V: Fields of Terror. She received her first big-screen break when she appeared in the award-winning and critically-acclaimed Training Day.
Along with acting, Mendes is employed by Revlon Cosmetics as an international spokeswoman. She joins such elite actresses and models as Julianne Moore, Halle Berry and Cindy Crawford, who appear in Revlon's television and print ads. She is also a passionate supporter and active participant in Revlon's fight against breast cancer.
"Maxim" ranked her #7 in its 2007 Hot 100 issue. Mendes also made her second Maxim cover in the November 2007 issue.
It was reported on January 31, 2008 Mendes had been in a rehab facility in Utah for several weeks. Her representative told TMZ that she has been "working hard for the past year and made a positive decision to take some much-needed time off to proactively attend to some personal issues that, while not critical, she felt deserved some outside professional support. Out of respect for Eva's privacy, we do not wish to discuss further details."
In August 2008, Mendes said she will not hesitate to get plastic surgery done when her figure starts to sag.