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.
The SABC will scale back on international content on its three entertainment TV channels in favour of locally produced programming. Read More »
In honour of pop icon, Prince, DStv will air an entertaining music special titled Prince: Behind The Symbol. Read More »
Cape Town show pics.
All the deets.
Live gig pics.
South AfricaCity Press
Johannesburg SouthAdendorff Machinery
Sea PointCape PlacementsR15 000 - R20 000 Per Month
FarmsR 3 250 000
HousesR 6 950 000
TownhousesR 1 399 000