George Horton will serve 10 months in jail and two years probation for six charges including mischief and assaulting a police officer.
Justice Beverly Brown said he covered his face with a bandana and kicked a police cruiser at Queen Street West and Spadina Avenue on June 26, 2010, knowing there was only one vulnerable officer in the car.
In his victim impact statement, Staff Sgt. Graham Queen said he feared for his life as protesters smashed the windshield and back window. He had been hit in the head with a pole that came into the cruiser and he believed another blow could have knocked him unconscious.
During the proceedings, two of Horton's supporters snickered and laughed. A detective sitting with Queen told them to be quiet. They cursed and were forcibly removed.
Later, other friends of Horton also cursed at the judge and were also removed.
Horton has been the only person convicted of assaulting a police officer during the G20 summit.