Leah Remini was born in Bensonhurst, Brooklyn, New York, to George Remini, an Italian-American owner of an asbestos company (not to be confused with the late Gambino crime family captain George Remini). Her mother Vicki Marshall, a former high school principal and current LA restaurant owner, is Jewish and originally from Austria.

Remini moved to Los Angeles at the age of 13. She tried fitting into her new neighborhood by imitating the look and style of the local Mexican-American culture. When Remini was 14, she left school against the advice of her mother.

At the beginning of her working life, Remini had a variety of jobs, such as waitressing, selling car insurance, and as a telemarketer for a solar heating company.

Remini's entrance into television came in the mid-'80s, when she got her first speaking line as an actress on an episode of Head of the Class. Later she was on the show Cheers where she appeared as Carla Tortelli's daughter Serafina on two episodes. Leah played the lead on Living Dolls, a short-lived spin-off from Who's the Boss? In 1991, she had a recurring role as Stacey Carosi, a love interest of Zack Morris, on Saved by the Bell (during the summer when the gang worked at the Malibu Sands Beach Club) and starred in the short-lived sitcom The Man in the Family. Remini also guest starred in The Commish, where her character was involved in the plot line responsible for Geoffrey Naufft's departure from the show. She gained some popularity with her role as Terri Reynolds on the 1997 NBC comedy series Fired Up. She starred as the main character Carrie in the TV sitcom The King of Queens.She had several guest appearances on shows such as Evening Shade, Diagnosis: Murder, NYPD Blue and Friends (in the Season 1 episode "The One with the Birth"). She originally auditioned for the part of Monica Geller but did not get the role. Remini has also made an appearance on MTV Cribs.

On July 19, 2003 she married actor Angelo Pagan. This was aired on the VH1 series Inside Out. On June 16, 2004, she gave birth to a daughter, Sofia Bella a day after her 34th birthday. This was chronicled on the VH1 documentary Inside Out: Leah Remini the Baby Special. Her weight has varied widely after the birth of her daughter, she was heard to lament on an episode of Fat Actress. Viewers of the King of Queens might note that Remini gained weight when she got pregnant during the middle seasons of the show, but lost the weight by the show's 9th and final season. Remini currently lives in Los Angeles, California with her family and her dog Blue. Remini is also good friends with Jennifer Lopezand her husband Marc Anthony. Remini is a member of the Church of Scientology.