The actress passed away in her sleep, her agent Craig Wyckoff said. No cause of death has been established and authorities has not issued a death certificate.
Kelly had voluntarily checked herself into a treatment facility early this week where she was battling addiction problems that have plagued her over the years, said Wyckoff.
“I spoke to her on Monday and she was hopeful and confident, looking forward to putting this part of her life behind her,” Wyckoff said.
Kelly, a Connecticut native, made her television debut in 1992 with “Married…with Children,” a Fox sitcom before playing Laurie Forman, the elder sister of the lead character in the iconic “That ’70s Show”.
The show focuses on the lives of a group of teenage friends living in the fictional suburban town of Point Place, Wisconsin. The cast also included Ashton Kutcher, Mila Kunis, Wilmer Valderrama and Topher Grace.
Kelly left the show after five years due to a drinking problem. Her role was replaced by Christina Moore.
Kelly had a number of problems with the law. She was arrested at least four times over the past three years over drunken driving, spousal abuse involving husband Robert Gilliam and assault.
She filed for divorce earlier this year and the case was still pending