To the victims of human rights criminals he was a crusading knight fearlessly wielding the sword of justice wherever it was needed across the globe. Now Judge Baltasar Garzón, the Spanish magistrate who pursued dictators, terrorists and drug barons, has himself been condemned in a remarkable court verdict that claims he behaved like the totalitarian regimes he famously pursued.

Garzón's career effectively came to a dramatic end on Thursday as he began an 11-year suspension for illegally wiretapping conversations between remand prisoners and their lawyers in a corruption case involving the prime minister, Mariano Rajoy's People's party (PP).

The furious reaction of Garzón's supporters and the euphoria of his enemies revealed bitter divisions over a man who first landed himself in trouble by investigating the abuses of Spain's former dictator, General Francisco Franco.

As his supporters gathered to demonstrate in Puerta del Sol square in central Madrid on Thursday evening, many claimed there was a conspiracy to bring down one of the world's best-known human rights investigators. They pointed to the unprecedented coincidence of a Spanish investigating magistrate being tried in three different cases of alleged abuse of authority at the same time.

"It was clear they were out to get him, and now they have," said Emilio Silva, head of the Historical Memory Association that campaigns to shed light on Francoist killings. "It is very sad. Plenty of other judges have committed the same irregularities and have not been treated this way."

"I cannot accept this," said Gaspar Llamazares, a deputy for the United Left party. Francisco Jorquera, a deputy for the Galician National Block party, claimed the sentence was a public lynching and proof of a vendetta against Garzón.

Reed Brody of Human Rights Watch said: "It looks like Garzón's enemies got what they wanted … the criminal prosecution of a judge for his judicial actions undermines the independence of the judiciary. The accumulation of charges against him raise the appearance that they have been brought in revenge for his handling of cases involving vested interests."

That he should be banned for investigating the sort of corruption that brought the country's indignados, or indignant ones, on to the streets in protest last year only added insult to the injury felt by some. The guilty verdict against Garzón, they pointed out, made him one of the first people to be punished in the long-running Gürtel case involving corruption in the PP regional governments of Valencia and Madrid.

The case alleges public money was siphoned off by PP politicians and crooked businessmen during, among numerous other cases, a visit to Spain by Pope Benedict. "Garzón has become the first victim of the Gürtel clan," the Garzón solidarity group, which called Thursday's protests, said.

Critics rejoiced at the downfall of a man they saw as vain, media-loving, transparently leftwing and a loose cannon in the Spanish judicial system.

"This puts things in their place," said José Antono Choclán, one of the lawyers.

"The judge stuck a finger up at our constitution, which ensures that all Spaniards have the same rights at trial," said Agapito Maestre on the rightwing Libertad Digital blog.

"It was about time," said Carlos Rodríguez in a fierce Twitter debate between supporters and detractors. "He thought he was Superman."

PP politicians struggled to hide their joy at the demise of a judge who, despite a stormy relationship with the Socialist party that once made him a parliamentary deputy, they felt was out to get them. "It is a happy day for the rule of law," said Esperanza Aguirre, the PP president of the Madrid regional government.

Even Garzón's supporters recognised he may have overstepped the mark by recording the conversations as he attempted to prove some lawyers were involved in money laundering, but they said the punishment was excessive.

"They could easily have come to the opposite conclusion," said José Antonio Martín Pallín, an emeritus supreme court magistrate. "This was an important investigation into organised crime and corruption."

Pallin pointed out that a second magistrate had ordered that the wiretaps continue. "If they were to be rigorous [in their logic], they would go after the other magistrate too," he said.

Garzón claimed he had put into place measures to safeguard the right of suspects to prepare their defence in private.

State attorneys had backed Garzón at his trial, saying investigating magistrates in other cases had made similar orders without facing charges.

But the supreme court said Garzón not only illegally wiretapped the prisoners' conversations but committed a second crime by doing so in the full knowledge that he was breaking the law.

"We shall carry on fighting, carry on appealing. We have a long road ahead, but I believe both he and I are more than strong enough," Garzón's lawyer, Javier Baena, said after the verdict.

Garzón cannot appeal in a Spanish court, despite insistence by the UN human rights committee (in a 2008 finding about a Spanish case) that this right should be available to everyone. He has previously said that he will take his case to the European court of human rights in Strasbourg if he has to.

The 56-year-old judge, best known for his groundbreaking use of international human rights law when he ordered the 1998 arrest of Chile's former dictator Augusto Pinochet, must also pay a €2,500 fine. That money reportedly goes to those at the centre of the Gürtel case.

• This article was amended on 13 February 2012. The original referred to insistence by the EU that the right of appear in a domestic court should be the right of Spaniards. This reference has been replaced by one concerning a similar stance adopted by the UN human rights committee.