Manager Craig Wyckoff says Kelly died on Wednesday at a Los Angeles addiction treatment facility she had entered early this week.
No official cause of death was disclosed.
Kelly portrayed Laurie Forman, sister of Topher Grace's lead character Eric, on the Fox series. It concluded in 2006.
Unlike some of her co-stars - Grace, Ashton Kutcher and Laura Prepon - Kelly fell out of the spotlight after appearing on the sitcom until she started making headlines for personal troubles.
She was arrested in November along with husband Robert Joseph Gilliam in connection with a disturbance at their home in North Carolina.
In June, she was arrested on suspicion of drunken driving after her car stalled in California.
TMZ has further details about her death - watch here:
24.com publishes all comments posted on articles provided that they adhere to our Comments Policy. Should you wish to report a comment for editorial review, please do so by clicking the 'Report Comment' button to the right of each comment.
Despite a cheering crowd welcoming Bill Cosby in Melbourne, Florida, the embattled entertainer's stand-up tour has crumbled with cancellations amid sex claims. Read More »
Bill Cosby has taken his comedy show on the road in the Bahamas as controversy surrounds him at home. Read More »
Watch this insane drift contest with four-times dirt-track World champion Karl Maier riding a speedway bike against a BMW M235i.
MpumalangaGreen Marble Recruitment ConsultantsR10 000 - R15 000 Per Month
GautengRivoni Recruitment & Talent Specialist CC
Northern CapeCozens Recruitment Group (Sandton)
HousesR 2 200 000
HousesR 2 600 000
HousesR 3 500 000