Born in Naugatuck, Connecticut, Bergin attended the University of Connecticut. He began modeling while in college.
Bergin is perhaps best known as Mark Wahlberg's successor in Calvin Klein's racy series of black and white underwear ads. In addition to his high-profile role as the "spokesbody" for Calvin Klein, Bergin has walked the runways of New York City, Paris and Milan for Sonia Rykiel, Valentino, Calvin Klein, Gianfranco Ferre, Giorgio Armani, Yves Saint Laurent and Donna Karan and was the exclusive model for Claiborne for Men, a division of Liz Claiborne, Inc., for over three years. He has also appeared in commercials and print advertisements for Kellogg's, Bacardi Rum, L'Oréal, Maybelline, Coty, Valentino, Perry Ellis, and Liz Claiborne. Bergin is signed to Wilhelmina Models in New York City, and New York Model Management.
Apart from the fashion industry, Bergin also ventured into acting, playing the character J.D. Darius on Baywatch and later Baywatch: Hawaii for 88 episodes from 1997 to 2001, and starring as the same character in the made-for-TV Film Baywatch: Hawaiian Wedding in 2003.
In 2006, he appeared on VH1's sci-fi celeb reality show Celebrity Paranormal Project. Bergin later launched his own brand of men's underwear.
Bergin now works as a real estate agent in Beverly Hills.
In the early 1990s, Bergin met Carolyn Bessette-Kennedy, a Calvin Klein publicist, whom he dated seriously, despite her burgeoning relationship with John F. Kennedy, Jr., whom she later married in September 1996. Kennedy and Bessette-Kennedy died in a plane crash in July 1999. In early 2004, Bergin published a book about his relationship with Bessette, The Other Man, claiming that they continued a sexual affair during the time Bessette was dating Kennedy and during their marriage.
On September 24, 2004, Bergin married makeup artist Joy Tilk with whom he has two children.
Bergin was arrested for drunk driving in 2004, on the fifth anniversary of Bessette-Kennedy's death.
Bergin has worked with the anti-drug children's program D.A.R.E. as a national spokesperson, and has lent his name, time, and image to numerous AIDS charities.