Jeff Goodman of Fox Sports first reported Stewart's decision.
While he must sit out the 2011-12 season per NCAA rules, the 6-foot-7 Stewart can redshirt this season and will have two seasons to play once eligible.
Stewart averaged 8.5 points and 4.4 rebounds per game last season, up from 7.3 points and 3.2 rebounds as a true freshman, while starting 16 of the 30 games he appeared in.
Stewart asked for his release from the Demon Deacons in March after his playing time decreased. He was held scoreless in his final four games before not playing in a first-round ACC tournament loss.
Stewart becomes the second prominent transfer brought to USC by coach Kevin O'Neill, joining Aaron Fuller of Iowa.
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