The opposition figure faces up to 10 years in prison for denouncing Putin’s war in Ukraine.
The trial against Yashin, a 39-year-old Moscow city councillor, begins during an unprecedented crackdown on dissent in Russia, most of whose opposition activists are either in jail or exile.
Yashin refused to leave after President Vladimir Putin sent troops into Ukraine on February 24.
He is an ally of jailed opposition leader Alexey Navalny and was close to Boris Nemtsov, an opposition politician assassinated near the Kremlin in 2015.
Standing in a defendant’s cage in Moscow’s Meshchansky District Court on Wednesday, Yashin was seen laughing, doing a thumbs-up and stretching, the AFP news agency reported.
Wearing a dark green hoody and jeans, he was also seen smiling at his parents in the front row.
Spreading ‘fake’ information
Yashin was arrested in June while strolling through a park in the Russian capital.
He faces up to 10 years behind bars on charges of spreading “fake” information about the Russian army under legislation passed after Putin launched the attack on Ukraine.
The reason for the case against Yashin is an April YouTube stream, in which the politician spoke about the “murder of civilians” in the Kyiv suburb of Bucha, where the Russian army has been accused of war crimes. He called it a “massacre”.
While in detention, Yashin has not minced his words about Russia’s tactics in Ukraine.
In a speech in court this month, he accused Russia’s judges of acting as “political servants of the Kremlin”.
Another Moscow councillor, Alexey Gorinov, was sentenced in July to seven years in prison for denouncing the Ukraine offensive.
The 61-year-old had questioned plans for an art competition for children in his constituency while “every day children are dying” in Ukraine.
Nearly all of Putin’s well-known political opponents have either fled the country or are in jail.
Navalny, 46, is currently serving a nine-year jail term on embezzlement charges widely seen as politically motivated.
Moscow has stepped up efforts to stamp out dissent since Putin launched the full-scale invasion of Ukraine.