Alexei Navalny, the anti-corruption campaigner who is a leading foe of Russian President Vladimir Putin, has been found guilty of fraud and given a suspended sentence.
Moscow's Zamoskvoretskiy court found the 38-year-old opposition leader guilty on Tuesday morning, but sentenced him only to three and a half years probation period.
However, the judge said his brother Oleg would have to serve the same period behind bars.
"Out of all types of verdicts, the most sneaky one was delivered today," said Navalny on his Twitter account.
The prosecutor was earlier demanding a 10-year prison sentence for the charismatic leader.
Al Jazeera's Peter Sharp, reporting from Moscow, said Navalny would stay under house arrest until his appeal against the guilty verdict in April.
"If it is upheld, he will be on probation deprived of any part that he could possibly play as the leading light in the political opposition in the next three and a half years," said Sharp.
Navalny, who has been under house arrest since February, already faced a five-year term over embezzlement last year, but walked away with a suspended sentence.
Along with his brother Oleg, Navalny was later accused of defrauding French cosmetics company Yves Rocher of more than $500,000. The firm has said that it suffered no damages.
Navalny and his supporters have said the case was an attempt to muzzle him. He shot to prominence during anti-Kremlin protests in 2011-12, which have since fizzled out under a crackdown. However, his influence increased again after he came second in the Moscow mayoral election last year.
Mass protests expected
Navalny's supporters are due to gather at Moscow's Manezh square, near Kremlin, at 16:00 GMT for a demonstration that some expected could turn into a wider anti-government protest.
Russian punk rock band Pussy Riot, a group of anti-Kremlin activists, have released a new video, calling for the rally as they dress up as witches sweeping Manezh square and flying on broomsticks over the Kremlin.
At least 16,000 people confirmed on the event's Facebook page before the announcement of the verdict that they are going to attend the protest.
The rally was initially planned for January 15 to coincide with the scheduled court verdict hearing, but trial date change prompted Navalny's supporters to swiftly re-group.
The demonstration could stir simmering discontent over the collapse of the rouble and growing inflation as oil prices tumble and Western sanctions over Ukraine take their toll.
For better coordination, Navalny urged his supporters to install on their phones the FireChat app - widely used by protesters in Hong Kong this year - if authorities move to jam mobile phone connections.