The lawsuit, filed Tuesday in Los Angeles by Daniel Refoua, accuses Stewart of assault, battery, false imprisonment, negligence and intentional infliction of emotional distress.
Refoua's lawyer, Sean Bral, said his client was beaten up Jan. 5, 2006, by a group including Stewart after accidentally bumping into the singer's son at Hollywood's LAX nightclub.
The melee followed an argument between Refoua and Stewart, who had a bodyguard with him, Bral said.
"The next thing you know, he gets punched in the face and he's getting punched by Stewart and his bodyguard and whoever it was who was with him," he said.
Refoua, who is in his 20s, suffered a fractured nose and other injuries, Bral said. The lawsuit seeks unspecified general, special and punitive damages.
"We invite him to come forward if they want a resolution in this, to sit down early to talk as opposed to later," Bral said.
Stewart's lawyer, Peter J. Korn, did not immediately respond to a phone message seeking comment.
Additional lawsuits may be filed against the others accused of attacking Refoua, Bral said.
The lawsuit comes about two months after Stewart, one of the stars of the Aamp;E reality show "Sons of Hollywood," was arrested in a separate attack on a couple outside a Hollywood Hills party.
The couple said they were in a truck in April when Stewart and others confronted them and began punching and throwing bricks at them and the vehicle.
Stewart has pleaded not guilty to felony charges in the case. He remains free on $60,000 bail pending a hearing Monday.
Korn said the incident is "much different" than what has been alleged in the complaint, and suggested the lawsuit was financially motivated.
Sean Stewart is Rod Stewart's son from his marriage to model-actress Alana Stewart. The couple divorced in the early 1980s.