Oleg Orlov, co-chair of the human rights group Memorial, went on trial in Moscow on Thursday over criticism of Russia's Ukraine campaign, which could see him jailed for up to five years.
AFP journalists at Moscow's Golovinsky district court reported the beginning of the trial, the latest in a series against Russian civil society organizations.
"All will be well," Orlov said, holding up his fist in a sign of defiance, while showing journalists a book titled "The End of Regime" by Alexander Baunov, on the fall of European dictatorships.
At the hearing, he was accompanied by Nobel Peace Prize winner Dmitry Muratov, who joined his defense team.
In an interview with AFP on the eve of the trial, Orlov said his defense would fight the "idiotic charges" he was facing.
Orlov was charged with repeatedly discrediting Russia's military over lone pickets against the Ukraine offensive and over an op-ed in French publication Mediapart titled "They wanted fascism, they got it."
He said he stood by his words but held no illusions on the outcome of the trial.
"Some may tell themselves that it is better to be silent. But my entire previous life and my position obliged me not to be," Orlov told AFP.
"The verdict will be guilty, no one has any doubt about it," Orlov said, wondering how harsh the sentence would be.
"I regret nothing, I will say that to the court."
His organization established itself as a key pillar in civil society by preserving the memory of victims of communist repression and campaigning against rights violations in Russia under President Vladimir Putin.
It had been dissolved in 2021 just months before Putin sent troops to Ukraine.
In March, charges of "rehabilitation of nazism" were brought against Memorial employees.
Since the beginning of the offensive, the Russian government has heightened its repression of critical voices with an array of legislation, including laws against discrediting the army.