ATHENS — An Athens court sentenced the leadership of Greece’s Golden Dawn party to 13 years in prison on Wednesday, a week after declaring the neo-fascist party a criminal organization in a landmark verdict that wrapped up one of the most important political trials in the country’s modern history.
Last week, the court convicted the party leaders of crimes related to a campaign of attacks against migrants and leftist critics in 2012 and 2013. At the end of a trial that lasted more than five years, the party was tied to a string of attacks, including the fatal stabbing in 2013 of a left-wing rapper, Pavlos Fyssas.
Giorgos Roupakias, a party member convicted of murdering Mr. Fyssas, received the harshest sentence, life plus 10 years. The court could still suspend some of the sentences.
The convictions were widely seen in Greece as a final blow to Golden Dawn, which failed to re-enter Parliament in general elections last year as the trial gradually eroded its popularity. And the outcome has already spurred political upheaval.
“The verdict sent a very clear message: We must guard against nationalism and racism,” said Seraphim Seferiades, an associate professor of politics and history at Panteion University in Athens. But “the far right is not dead because of a judicial decision,” he said. “The danger will always be there unless the underlying issues are addressed.”
In all, the court convicted 50 people of membership in a criminal organization — 18 of them former politicians for Golden Dawn including its leader, Nikos Michaloliakos.
In addition to Mr. Roupakias’s conviction, five other party supporters or members were found guilty of the attempted murders of three Egyptian fishermen in 2012. Four others were convicted of causing bodily harm in assaults on members of Greece’s Communist Party trade union in 2013.
Mr. Michaloliakos and five other former members of Parliament for Golden Dawn were all sentenced to 13 years in prison. One other former lawmaker who was among the party leaders was sentenced to 10 years in prison. The group’s remaining 11 former lawmakers to be sentenced received prison terms of five to seven years.
Before the sentences, defense attorneys had urged the court to consider mitigating circumstances, citing good character, lawful behavior and, in some cases, their clients’ marriages to foreign women.
The party’s leadership was arrested in September 2013, a few days after the killing of Mr. Fyssas — the first time a leader of a Greek political party and its members of Parliament were arrested since the fall of the country’s military dictatorship in 1974.
Some of them already served the legal maximum of 18 months in pretrial custody and were then released — time that is due to be deducted from their sentences.
After the sentences were announced, the court was to deliberate on whether to suspend any of them, a decision that may not come until Thursday. If the court deems any of those convicted not to be a flight risk, it might allow their sentences to be suspended pending the outcome of their appeals.
Golden Dawn’s fall was as spectacular as its rise. It was catapulted from obscurity into the front line of Greek politics at the peak of the country’s financial crisis in 2012-2013 by tapping into public discontent over austerity measures and a growing influx of migrants.
Mr. Seferiades said a failure by successive governments to alleviate the impact of years of austerity, and by the European Union to find a humane solution to the migration problem, had helped “normalize racist discourse.”
“Everybody knew about Golden Dawn since the ’80s, but there was no political response,” he said, adding that the 2013 crackdown was a reaction to a public outcry over the death of Mr. Fyssas, the rapper. The government “finally reacted because they ran the risk of a social uprising which they could not have handled.”
In spite of Golden Dawn’s dramatic decline, neo-Nazism in Greece has not disappeared. Former members of Parliament, including Ilias Kasidiaris, Golden Dawn’s onetime spokesman, have formed parties that embrace similar views.
Less extreme right-wing parties have also sprung up, including the nationalist Greek Solution.
In a post on Twitter last week, Mr. Michaloliakos, the party’s leader, said Greeks would remember Golden Dawn “when illegal immigrants are the majority in Greece, when they concede earth and water to Turkey, when millions of Greeks are unemployed on the streets.”
He was referring to arrivals of migrants from Turkey and a recent political crisis between the two neighbors over longstanding territorial disagreements and corresponding energy rights.
Mr. Michaloliakos insisted that the party was the victim of a witch hunt.
In the immediate political fallout from the convictions, former Justice Minister Stavros Kontonis resigned last week from the central political committee of the main leftist opposition party, Syriza and was subsequently ejected from the party. In addition to infighting within the party, he cited concerns that a criminal code introduced last year by the previous leftist administration could lead to lighter sentences for Golden Dawn.
Among other things, the code would treat the leader of a criminal organization the same as any other member, he said.
The governing conservative New Democracy party responded that Mr. Kontonis’ comments “exposed Mr. Tsipras’ blatant cynicism and profound hypocrisy,” referring to the leader of Syriza, former Prime Minister Alexis Tsipras.
“He stood outside the appeals court demanding the conviction of Golden Dawn’s officials,” the party said, “when, as prime minister, he had ensured a ‘softer fall’ for them.”