It is a further step in a year-long, multi-pronged crackdown on Russia's most prominent Kremlin critic, his allies and other dissenting voices.
Navalny, President Vladimir Putin's long-time opponent, is charged with fraud and contempt of court. His allies denounced the case as an effort by the Kremlin to keep the politician in prison for as long as possible.
Authorities moved the trial to the prison colony hours away from Moscow, where Navalny is serving a sentence for parole violations. The move was criticised for effectively limiting access to the proceedings for the media and supporters.
The 45-year-old appeared in the makeshift courtroom wearing a prison uniform.
"It is just that these people, who ordered this trial, are really scared," he said during the hearing. "(Scared) of what I say during this trial, of people seeing that the case is obviously fabricated."
The trial got under way with world leaders preoccupied with another round of tensions between Moscow and the West fuelled by fears that Russia plans to invade its ex-Soviet neighbour Ukraine.
Navalny could receive up to 15 years in prison if convicted, his allies said, on top of the time he was ordered to serve last year.
He was arrested in January 2021 on his return from Germany, where he spent five months recovering from a nerve agent poisoning he blames on the Kremlin, accusations Russian officials denied.
Shortly after the arrest, a court sentenced him to two-and-a-half years in prison over the parole violations stemming from a 2014 suspended sentence in a fraud case Navalny insists was politically motivated.
Authorities then unleashed a sweeping crackdown on his associates and supporters. His closest allies have left Russia after facing multiple criminal charges, and his Foundation for Fighting Corruption was outlawed as extremist.
Russian officials this month added Navalny and a number of his associates to a registry of extremists and terrorists.
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