Navalny, who is a strident critic of President Vladimir Putin, was found guilty of large scale theft in a trial he says was politically motivated.
Prosecutors at the court in Kirov, 500 miles north-east of Moscow, had asked the court to jail Navalny for six years.
The guilty verdict could stop him challenging Putin in the 2018 presidential election.
Navalny was found guilty of embezzling 16 million roubles from a timber firm while advising the region’s governor in 2009.
The Kremlin critic first came to prominence in 2011, when he was one of the leaders of mass street protests against the results of parliamentary elections. He is also an anti-corruption blogger.QHA