Fonda was born in Los Angeles, California into a family of actors, including her grandfather Henry Fonda, her father Peter Fonda, and her aunt Jane Fonda. Her mother, Susan Jane Brewer, is an artist. She is named after actress Margaret Sullavan's daughter Bridget Hayward who committed suicide at the age of 21. Sullavan was Henry Fonda's first wife. Bridget's parents divorced and Peter remarried Portia Rebecca Crockett (former wife of author Thomas McGuane). Peter and Portia brought up Bridget, her brother Justin, and older stepbrother Thomas McGuane Jr (born circa 1962) in the Coldwater Canyon section of Los Angeles as well as just south of Livingston, Montana, where both brothers attended high school. Fonda attended Westlake School for Girls in Los Angeles