Alexander Kozulin, 50, a former presidential candidate and leader of the Social Democratic Party, was arrested during protests March 25 against the results of the March 19 presidential elections that saw President Alexander Lukashenko re-elected to a third term. Kozulin's trial began July 6.
Kozulin was convicted on charges of hooliganism, violating public order and refusing to obey law enforcement officers. By law, the charges against him provide for a sentence ranging from a fine to six years in prison.
Prosecutors requested a six-year term for the opposition leader.
His defense lawyers appealed the ruling, saying the verdict is too harsh for Kozulin, who is innocent.
Igor Rynkevich, a lawyer, said Tuesday the defense team asked the court "to drop the criminal case against Kozulin, release him and stop persecuting him."
Lukashenko, whom Washington dubbed "Europe's last dictator," was re-elected to a third term with a massive 83% of the vote. Although he has support in his homeland for maintaining relative stability in comparison with some other former Soviet republics, his human rights record has been fiercely criticized by international organizations.
The March elections were denounced by the opposition and international monitors as fraudulent, and opposition activists staged a five-day sit-in in Minsk's central Oktyabrskaya Square.
A demonstration March 25 was broken up by police, and opposition representatives say at least one person died as a result.