Chabert made her start as young Cosette in Les Misérables on Broadway. Chabert was a member of the Broadway Kids which included Christy Carlson Romano, Chris Trousdale, and Greg Raposo. She was originally selected to play the role of "Young Lily" in the movie Return to the Blue Lagoon (1991), but bailed out for unknown reasons. Chabert then landed the role of Bianca Montgomery on the ABC soap opera All My Children in 1993. Chabert became famous worldwide for her role as Claudia Salinger in the TV drama Party of Five, "I had to go through everything on that show—my first kiss, my first bra. I was 11 when it started," she said. She also gained fame for her portrayal of Penny Robinson in the 1998 film Lost in Space, based on the 1960s television show. Lacey Chabert also played in Hometown Legend as Rachel Sawyer.

Since 1998, she has been the voice of Eliza Thornberry in the animated series The Wild Thornberrys; she also voiced Eliza in two Wild Thornberrys movies, The Wild Tho