Yevgeny Urlashov made headlines when he quit the ruling United Russia party and beat its candidate in 2012 mayoral polls in Yaroslavl, a city north of Moscow, in which he was endorsed by Russia's top opposition figures.
He was then arrested in July 2013 and accused of extorting 18 million rubles (USD 270,000) from a businessman.
"The court has sentenced Urlashov to 12 years and six months in a penal colony and ordered him to pay a 60-million-ruble (USD 900,000) fine," court spokeswoman Anna Mochinova told AFP.
Russia's powerful investigative committee on Wednesday accused Urlashov of taking a 17-million-ruble bribe from a construction company.
Urlashov has denied all charges.
His lawyer Ksenia Karpinskaya told RIA Novosti that the defence would appeal the sentence, which she said was "not only unfair but also cruel."
Urlashov's former advisor, Alexei Lopatin, was sentenced to seven years, investigators said.
At the time of Urlashov's arrest, masked men raided city hall in Yaroslavl, which has a population of 600,000 and is located about 300 kilometres (190 miles) north of Moscow. Urlashov said his arrest was an attempt by corrupt businessmen to oust him.
