The court also convicted Vladimir Arutyunian for killing a policeman in the course of an operation to arrest him several weeks after the May 10 incident.
Mr. Bush and Saakashvili were addressing a rally of thousands in Tbilisi from behind a bulletproof barrier when the grenade, wrapped in a cloth, landed about 100 feet away. It did not explode, and investigators said it apparently malfunctioned. No one was harmed.
Arutyunian was arrested in July on the outskirts of Tbilisi after a shootout that killed one officer. Arutyunian was later shown in television footage from a hospital bed admitting that he had thrown the grenade, throwing it high with the aim of having it explode so that the bulletproof glass would not block shrapnel.
Arutyunian, whose trial began last month, has acknowledged that he threw a grenade in the direction of the stage and said he would try again to kill Mr. Bush if he had the chance.
Mr. Bush and Saakashvili learned of the incident only after the rally.