At age 21, Diaz auditioned for The Mask, based on the recommendation of an agent for Elite, who met the film's producers while they were searching for the lead actress. Having no previous acting experience, she started acting lessons after being cast. The Mask became one of the top ten highest grossing films of 1994. and launched Diaz as a sex symbol.
Diaz's only film of 2007 was Shrek the Third, the third installment in the Shrek franchise. Although the film was met with mixed reviews from critics, in contrast to the critical acclaim achieved by the previous films, it grossed $798 million worldwide. The same year, Diaz also voiced Princess Fiona in a thirty-minute Christmas special, directed by Gary Trousdale. Diaz reportedly earned $50 million during the period of a year ending June 2008, for her roles in the Shrek sequel and her next film What Happens in Vegas opposite Ashton Kutcher. A romantic comedy by Tom Vaughan, Diaz and Kutcher portrayed two strangers who awaken together to discover they have gotten married following a night in which they won a huge jackpot after playing the other's quarter. While audiences reacted positively to the film, reviews were negative.
In 2009, she starred in My Sister's Keeper and The Box. Based on Jodi Picoult's novel of the same name,My Sister's Keeper was released to mixed reviews in June 2009. In the drama, Diaz plays a former lawyer and mother of two, one of whom is dying of leukemia. A moderate commercial success, it grossed $95 million worldwide, mostly from its domestic run. Set in 1976, The Box, written and directed by Richard Kelly, stars Diaz and James Marsden as a couple who receive a box from a mysterious man who offers them one million dollars if they press the button sealed within the dome on top of a box, knowing that someone, somewhere, will die from it. Critical response towards the psychological horror film was mixed, and, though having grossed its budget back, was considered a financial disappointment.
In 2010, Forbes ranked Diaz as the richest Hispanic female celebrity, ranking her number 60 among the wealthiest 100. Also that year, Diaz reprised her voice role of Princess Fiona in Shrek Forever After, the fourth installment in the Shrek series. Although the film opened to mixed reviews from critics, it grossed a worldwide total of over $752 million and became the fifth top grossing films released that year. Also in 2010, Diaz reunited with her Vanilla Sky co-star Tom Cruise in the action comedy film Knight and Day. In it, Diaz plays a classic car restorer who unwittingly gets caught up with the eccentric secret agent Roy Miller, played by Cruise, who is on the run from the Secret Service. Knight and Day received mixed reviews, and while the comedy performed poorly at the box office in its debut, it became a sleeper hit at the box office at a worldwide gross of $262 million.
In 2011, she played Lenore Case, a journalist, in the remake of the 1940s filmThe Green Hornet. Directed by Michel Gondry, Diaz starred alongside Seth Rogen, Jay Chou, and Christoph Waltz in the superhero action comedy film. Released to mixed to negative reviews from critics, who called it an "overblown, interminable and unfunny update", the film ended its theatrical run on April 21, 2011, with a worldwide gross total of $228 million. The same year, she played opposite Justin Timberlake and Jason Segel in Jake Kasdan's adult comedy Bad Teacher. In the film, Diaz plays an immoral, gold-digging Chicago-area middle school teacher at the fictional John Adams Middle School who curses at her students, drinks heavily, and smokes marijuana. Again, it received mostly negative reviews from critics who felt that "in spite of a promising concept and a charmingly brazen performance from Diaz, Bad Teacher is never as funny as it should be." A commercial hit however, the R-rated comedy grossed $216 million worldwide. Also in 2011, Diaz was listed among CEOWorld magazine's Top Accomplished Women Entertainers.
Diaz's first film of 2014 was the romantic revenge comedy The Other Woman opposite Leslie Mann and Kate Upton. Primarily filmed in Downtown Manhattan, New York City, it depicts Diaz as a successful, strong-minded lawyer, who discovers her boyfriend is married, only to bond with his wife and another woman she discovers he has been cheating with. While The Other Woman received mostly negative reviews from critics, who felt that it settled for cheap laughs, it opened atop the US weekend box office with earnings of $24.7 million across the three days. Also in 2014, Diaz starred in the comedy Sex Tape, with Jason Segel, and co-starred in another adaptation of the musical, Annie, playing Miss Hannigan.
Diaz received substantial defamation damages from suing American Media Incorporated, after the National Enquirer posted an article and pictures with the headline “Cameron Caught Cheating” on their website in May 2005. The photos claimed to show Diaz cheating on her boyfriend of the time, Justin Timberlake, with the married MTV producer of her show Trippin', Shane Nickerson. After Diaz complained, the article and pictures were removed from the web and the hard copy did not contain any of the content. The magazine apologized to Diaz, Timberlake, Nickerson and his wife for the distress caused and said the story was untrue and the picture showed no more than a goodbye hug between friends.
Diaz has publicly revealed that she suffers from ADHD, which prevents her from directing movies.
Diaz has been involved with the Iraq and Afghanistan Veterans of America (IAVA), the first and largest nonprofit organization for veterans of the wars in Iraq and Afghanistan, and has spoken as an advocate for military families. Although she was quoted by a 1997 Time article as saying she was germophobic, in 2009, Diaz specifically stated that a small comment she made 12 years earlier regarding public-bathroom doorknobs was distorted.
On April 15, 2008, Diaz's father, Emilio Diaz, died at the age of 58 from pneumonia.
In February 2015, Diaz spoke of the effect of practicing Transcendental Meditation, saying, "To have that tool now and to be able to go inside to the deepest part of myself and to access that and to recharge my battery internally, within myself, I feel so badass. I really do. I think it's so awesome. I feel so empowered that I actually possess that."