In an email sent to supporters, the 40-year-old said: "Presidential polls will take place in our country in 2018 and I have decided to take part in them."

His presidential bid was trending on Russian Twitter on Tuesday afternoon and his campaign video had been viewed more than 122,000 times.

It started with a blog

Navalny first became known for his blogs exposing Russian corruption, targeting Russian business and later major political figures.

Powerful figures targeted by Navalny mostly simply deny his accusations, but revelations in his blog have led to resignations, a rare occurrence in Russian politics.

Crowd funding

Navalny ran against Sergei Sobyanin, the pro-Putin incumbent, in the 2013 Moscow mayoral elections and surprised many by receiving more than 30 percent of the vote.

He raised about $2 million from a crowd-funding drive to pay for the campaign, which grew into a large operation driven by young volunteers.

A liberal-left-nationalist?

A group of prominent businessmen have said they will back Navalny - a Muscovite who holds degrees in law and finance.

For many years he attended the Russian March - an annual demonstration also attended by extreme nationalist groups - and has campaigned against subsidies that Moscow provides to Chechnya and other republics in Russia's North Caucasus.

In his presidential program he called for new restrictions on immigration and the introduction of visas for migrants from ex-Soviet nations in the South Caucasus and Central Asia. 

Russia's oil and gas revenues should be used "to create modern infrastructure - hospitals, schools and roads - not to build luxurious palaces for officials," he said in his campaign statement.

He also promised to stop Russia "throwing away" money on conflicts in Syria and Ukraine - where Russia denies its troops have backed pro-Moscow separatists.

Barred from running?

Navalny is undergoing a re-trial in the city of Kirov after Russia's Supreme Court overturned his conviction on fraud charges in a 2013 case. If the court re-instates his conviction, it will bar him from running for public office.

Since becoming one of the leaders of Russia's anti-Putin protest movement in 2011 he has been subject to repeated accusations of corruption, which his supporters say are politically motivated. He has served several short stints in jail.

Putin not too put out

President Vladimir Putin has not yet confirmed his candidacy but is expected to stand in 2018 for a fourth term. If he wins, he could rule until 2024, when he would turn 72.

Kremlin spokesman Dmitry Peskov declined to comment on Navalny's bid.

The Levada independent polling agency in November gave Putin an 86 percent approval rating.

Opponents to Putin's rule have been few and far between and the chances of overcoming a Kremlin-backed media and state apparatus are widely considered insurmountable.

jbh/kl (AP, dpa, AFP)