Bibb was born in Bismarck, North Dakota, and raised in Nelson County, Virginia. Her father died three years after she was born. Bibb subsequently moved to Richmond, Virginia, with her widowed mother and three older sisters, where she attended the all-girl Saint Gertrude High School. In 1990, The Oprah Winfrey Show and the Elite Agency held a nationwide modeling search. The celebrity judges, John Casablancas, Naomi Campbell, Linda Evangelista, and Iman chose Bibb as the winner. After finishing her junior year, Bibb flew to New York City to sign a contract with Elite Agency and modeled over that summer and went on a trip to Japan. Bibb returned to America for her senior year and graduated in 1991. Bibb later decided to attend the University of Virginia. After a single semester, however, Bibb abandoned her studies and moved to New York City to pursue her full-time modeling career. Bibb's modeling photographs have appeared in the magazines Maxim and FHM. She also attended the William Esper acting studio for three years.
After one episode roles on the television series Pacific Blue and Home Improvement, Bibb's first film role came in the comedy Private Parts. This was followed by her first television series, where she replaced the departed Susan Walters as the female lead in the second season of The Big Easy. Most critics panned the show, and it was canceled months later after low ratings. She appeared in the romantic drama Touch Me, co-starring Amanda Peet, Michael Vartan and Peter Facinelli. Later she portrayed a supporting role, Summer, in the film This Space Between Us, released in 1999.
In 1999, Bibb had her big break appearing as a lead character on the WB Network television series Popular. Her role was Brooke McQueen, the most popular girl at Kennedy High School who is beautiful, a straight-A student, and a cheerleader. The show was a major success among teenagers and led Bibb to more recognizable film roles. The show garnered her a Teen Choice Award for Television Choice Actress and a Young Hollywood Award nomination for Exciting New Face – Female. During the series, she filmed the horror–thriller The Skulls – released in 2000 – which co-starred Paul Walker and Joshua Jackson. Her character was Chloe, the classmate, friend and love interest of Jackson's character. The Skulls received a negative reception from critics but was a box-office success. She received a role in the 2001 comedy See Spot Run. Her role in the film was Stephanie, a single mother who spend most of the film on her own "Planes, Trains and Automobiles".
Bibb was cast in a recurring role on the series ER, and played the lead character on the television series Line of Fire. She also had a one-episode appearance on CSI: Miami. Bibb joined the cast of Crossing Jordan as Detective Lu Simmons until Season 6.
She appeared as Desiree in the independent film Wristcutters: A Love Story opposite Patrick Fugit, Shannyn Sossamon, Tom Waits, and Will Arnett. Wristcutters revolved around two characters who fall in love in purgatory after committing suicide. It was shown at both The Sundance Film Festival and The Seattle International Film Festival Awards in 2006. It was nominated for several awards including Sundance's Grand Jury Prize, two Independent Spirit Awards, the Humanitas Prize. The film was well received by several critics. That year, she played as Will Ferrell's wife Carley in the comedy feature film Talladega Nights: The Ballad of Ricky Bobby. Recalling acting with Ferrell during an interview with TV Guide, she said he was "just funny. And he has no qualms about making something funnier for you, even at his expense."
Bibb also starred in the sitcom Atlanta, opposite Freddie Prinze, Jr.. Her character was Jessica, a potential love interest for Prinze's character, meeting him at a funeral.
She was cast as Dr. Miranda Storm in Sex and Death 101, a black comedy, which was released direct-to-video in 2007. She appeared as a Vanity Fair reporter named Christine Everhart in the action film Iron Man (2008). In an interview, Bibb said about her character in the film: "she has a very strong sense of right and wrong, of good and evil, and I loved her passion." Iron Man received generally favorable reviews and grossed over $585 million worldwide. That same year, she portrayed the character of Maya in the horror–thriller The Midnight Meat Train, opposite Bradley Cooper. The film was promoted at the 2007 Comic-Con International, however, received a limited release in 2008. She also had the role of Emma in the direct-to-video horror film Trick 'r Treat, which was released in late 2008.
In the comedy Confessions of a Shopaholic (2009), she portrayed the rival of the main character, played by Isla Fisher. Confessions of a Shopaholic was panned by film critics, however, was a success at the box office. She had a pivotal recurring role on the NBC series Kings as Katrina Ghent, and played as Sarah Lowell in the thriller film Law Abiding Citizen (2009), which was released on October 16, 2009. The film was poorly received by critics.
In 2010, she reprised her role in the sequel to Iron Man, Iron Man 2. The film is Bibb's biggest box office success, with a worldwide gross of $621.8 million. Later in 2010, she starred opposite Adam Goldberg and Kathy Baker in the independent comedy Miss Nobody, in which she also served as co-producer. For her performance she won the Best Actress Award at the 26th Boston Film Festival. She was praised by critic Alissa Simon of Variety, who wrote "as she proved in Goran Dukic's Wristcutters: A Love Story, statuesque star Bibb is a smart actress willing to give herself totally to a role. As the sweetly goofy murderess, she takes pratfalls, suffers endless groping and sports unbecoming attire." Bibb also appeared in Kevin James' The Zookeeper, released on July 8, 2011.
It was announced that Bibb stars in the neo-noir thriller film Meeting Evil. Luke Wilson and Samuel L. Jackson also co-star in the film. Bibb and Jackson have appeared in the Iron Man film series. In 2012, Bibb starred as Amanda Vaughn on the ABC-TV series GCB, which debuted on March 4, 2012 but the show was cancelled after 10 episodes.
Bibb starred in the Neil LaBute play, Reasons to be Happy, which premiered in June 2013 at MCC Theatre in New York. It also featured Jenna Fischer, Josh Hamilton and Fred Weller.
In 2016, she starred as the antagonist in the YouTube Red original show Rhett and Link's Buddy System.
Bibb is a supporter of Friends of El Faro, a grassroots non-profit organization that helps raise money for Casa Hogar Sion, an orphanage in Tijuana, Mexico. In 2008, Revlon announced that its Almay Brand has signed Bibb as its ambassador. She acts as a spokeswoman for Revlon's new and existing cosmetics collections. She has appeared in global multi-media campaigns. In Fall 2010, Bibb became partner with the nonprofit LIFE Foundation by serving as the national spokesperson for Life Insurance Awareness Month. She posed nude for the May 2012 issue of Allure magazine.
Bibb married investment banker Rob Born on November 22, 2003, in Zihuatanejo, Mexico. The couple divorced on December 7, 2004. She has been in a relationship with actor Sam Rockwell since 2007, when they reportedly met in Los Angeles as he was filming Frost/Nixon. They both appeared in Iron Man 2.