Born and raised in Montreal, Quebec, Canada, by an American father and a Canadian mother, Caroline Rhea is fluent in French and English. Rhea moved to New York in 1989 to study stand-up comedy at the New School for Social Research. She says her true training came from her first gigs at the comedy club Catch A Rising Star. Performing around New York City, she quickly gained a reputation, and a name in the city's competitive comedy scene. These performances were augmented with appearances on MTV's Half-Hour Comedy Hour, Comic Strip Live and Caroline's Comedy Hour.

Rhea then decided to move on to Los Angeles for a career in Hollywood, debuting in the NBC television series Pride and Joy co-starring with Jeremy Piven. She gained fame for her role as Aunt Hilda on the ABC and The WB's "Sabrina, The Teenage Witch", as well as being a regular on Hollywood Squares, with Tom Bergeron and Whoopi Goldberg.

Some of Rhea's other credits include the films "Man on the Moon", "Christmas With the Kranks", and "Ready to Rumble", being host of VH1 series "Fool for Love", hosting the Lifetime series "The Great Lifetime Makeover", guest-starring as Drew Carey's girlfriend on "The Drew Carey Show", guest-starring on HBO's Larry David written show "Curb Your Enthusiasm", starring in television movie, "Mom's Got A Date With A Vampire", being a regular guest on "Late Night with Conan O'Brien", and making appearances on "The Late Show with David Letterman", "The Tonight Show with Jay Leno", and Comedy Central's "Pulp Comic". Rhea has also appeared in "Comic Relief 8", as well as the Ms. Foundation's "Women of Comedy from Caroline's Comedy Club".

Rhea also hosted "The Caroline Rhea Show" which was created in 2002 upon Rosie O'Donnell's departure from daytime television. Rhea had previously served as a guest host for O'Donnell throughout the final two seasons of The Rosie O'Donnell Show. The show was cancelled in June 2003, upon the completion of its first season.

In 2004, Rhea began hosting "The Biggest Loser"- a reality television show in which contestants are put through training and dietary regulation in order to lose weight.