Saakashvili, who led the Russia-critical so-called Rose Revolution in Georgia in 2003, has already been imprisoned for several years.
In 2021, he was sentenced to six years in prison, which he has largely served in a prison hospital after repeated hunger strikes. Now the sentence is being extended by three years.
When Wednesday's verdict was announced in Tbilisi, protests erupted in the courtroom, reports the Georgian news agency Interpress News. Supporters of Saakashvili, who believe the charges are politically motivated, called the judge "Bidzina's slave".
The Russia-friendly former Prime Minister Bidzina Ivanishvili is considered the de facto leader of the ruling party Georgian Dream. In recent years, the party has steered Georgia increasingly towards Moscow, despite ongoing popular protests demanding EU membership.