Thousands of anti-racism protesters had gathered outside the court in Athens where verdicts were delivered against dozens of people.
Police fired tear gas into the crowd after some hurled petrol bombs at officers.
The criminal investigation into Golden Dawn began after the murder of an anti-fascist rapper Pavlos Fyssas in 2013.
On Wednesday, a party supporter was found guilty of the killing and faces a life sentence behind bars.
Golden Dawn's leader Nikos Michaloliakos and other top members of the party were convicted of heading a criminal group.
They face jail sentences ranging from five to 15 years.
Golden Dawn entered parliament in 2012 on the back of an anti-austerity and anti-immigrant agenda and became Greece's third most popular party at the peak of the financial crisis in the country.
But the party failed to win a single parliamentary seat in last year's elections.
Prosecutors had charged 65 people, including 18 former Golden Dawn politicians, with being members of a criminal group.
When the trial started in 2015, the party said it was the victim of a politically motivated witch-hunt.
Dozens of those on trial, including party members and alleged associates, face charges that range from murder to perjury linked to a spate of violent attacks on immigrants and left-wing activists.
Protesters outside court held up banners reading, "Fascism Never Again".
Human rights group Amnesty International, which set up a network to record racist violence in Greece, said Wednesday's verdicts would help boost efforts to fight hate crimes.