The reading of the verdict took more than an hour. Arutyunian's lawyers said they would appeal against the sentence.
Although Arutyunian initially confessed in a police video to throwing the grenade with a view to hurting Bush, he pleaded not guilty at his trial.
Georgian prosecutors say the grenade Arutyunian tossed at Bush and his Georgian counterpart Mikheil Saakashvili during a 10 May public appearance did not go off for technical reasons.
(Prime News/Rustavi 2/AP)