Alexei Navalny is a busy man. He is running a campaign to become mayor of Moscow. He is managing a dozen young corruption fighters uncovering wrongdoing among the highest echelons of Russia's government. In his spare time, he is tweeting and blogging with fury, helping to spread his message that it is time to "destroy the feudal system of power" that has occupied the Kremlin.

What he is not doing is preparing for what appears to be inevitable.

Next Thursday, a judge in the provincial city of Kirov, 500 miles north-east of Moscow, will decide Navalny's fate. The 37-year-old father-of-two now faces the very real prospect of becoming the latest – and most high-profile – critic of Vladimir Putin to be thrown into prison as the Russian leader continues an unforgiving campaign to silence those who have dared to rise up against him.

The threat of jail has been hovering over Navalny since he first burst on to the scene in the winter of 2010. His investigations into corruption by everyone from state-run companies to Kremlin-loyal MPs put him in the crosshairs of a government that has never brokered those who challenge it.

"They don't like any phenomena or structures that they cannot control," Navalny said in an interview this week at his busy offices in central Moscow. "[Putin] wants to be president of Russia until his death, to be this kind of lifelong emperor."

Navalny's anti-corruption campaign won him a loyal following, with thousands of Russians donating to his cause. He took to social media early, winning hundreds of thousands of followers, to circumvent the state's stranglehold over television and, increasingly, print media.

When Moscow erupted in protest in the winter of 2011, as Putin prepared to return to the presidency amid accusations of voter fraud and creeping tyranny, Navalny became their de facto leader, working crowds into a frenzy with his fiery speeches calling for the people to take the power that was rightfully theirs.

"Everyone was always asking: When will they come [for me]? And now you think: Well, here they've come," he said.

Russia issued its first charges against Navalny in July 2012, just two months after Putin took power in an inauguration accompanied by unprecedented unrest. Riot police battled protesters who refused to accept the fact that the man who had ruled Russia since 1999 was intent on ruling for six, possibly 12 more years.

He has now lost count of how many charges he faces and is the target of endless official harassment. Sitting with the Guardian on Tuesday, he was interrupted by an official from the Investigative Committee, the closest thing Russia has to a political police, seeking documents about his anti-corruption fund, RosPil.

That might soon be a thing of the past.

For three months, Navalny, his wife and supporters have travelled hours by train to and from Kirov to attend hearings in his embezzlement trial. They've sat in a stuffy courtroom and listened to witnesses for both the defence and the prosecution argue in his favour.

It seemed that almost everyone in the courtroom agreed that the charges – that he embezzled 16m roubles' (£330,000) worth of timber while advising the Kirov region's liberal governor, Nikita Belykh, in 2009 – were fabricated.

Then last week, the state's prosecutor asked judge Sergei Blinov to hand Navalny a six-year sentence, accompanied by a 1m rouble fine.

Navalny makes his closing remarks in the court in Kirov. Photograph: Sergei Brovko/AFP/Getty Images

That Navalny will be found guilty is taken as a given: less than 1% of Russian trials end in acquittal and Blinov has never issued a not-guilty verdict in his career.

At best, he will be found guilty and given a suspended sentence – allowed to walk free but banned, by law, from participating in elections and destroying his official political career before it was really allowed to begin.

At worst, he will be sent to one of the remote Russian prisons that increasingly house those who challenge Putin.

"This decision will be taken personally by Putin," Navalny said.

Thousands of Navalny's supporters have vowed to gather outside the Kremlin's walls on Thursday to protest against a verdict that many already expect. No one knows how Russia's infamous riot police will react.

Navalny said: "They want to [jail me] but they're scared of it too."

Meanwhile, Navalny continues to live as if his life weren't hanging in the balance.

On Wednesday, accompanied by dozens of supporters, he marched to Moscow's election commission to present papers allowing him to register to run as a candidate in the city's September mayoral vote. He continues to advertise his platform, gather volunteers and spread the message that life in the city can change for the better even though he knows his chances of running in the race are near nil.

"For every person, of course, hope dies last," Navalny said. "Since you feel absolutely not guilty and know that everyone around you considers you absolutely not guilty, then in the depths of your soul somewhere you hope that the judge will come out, take out his hammer and say 'not guilty'," he said. "And something will happen like in American films and everyone will start hugging.

"But we all understand that this wasn't all started so that everyone would hug like in American films," he said, in the sarcastic tone filled with pop culture references that has become his trademark.

Yevgenia Albats, the editor of the New Times, Russia's leading opposition magazine, said Navalny has been targeted because the Kremlin fears him. "They understand his potential," she said, calling him "smart, honest, and a little bit populist".

His image as the "anti-Putin" has won him many supporters among both liberals who back his anti-Kremlin politics and other Russians drawn to his at times worryingly nationalist bent.

He appears everywhere with his statuesque wife, Yulia, in stark contrast to Putin, who hid his wife for years before finally announcing their divorce earlier this year. He uses the language of youth, peppering his anti-Putin speeches with references to the TV show Breaking Bad and posting pictures of cats during boring spells in his trial.

He is now paying the price for that popularity.

"Putin wants the period of his rule to be safe for him so he wants to control everything that is happening," Navalny said. "For a time he could do that via TV propaganda and through the support of the population that he got thanks to better quality of living.

"From 2003 to 2010 there was a lot of talk that Putin was ruling with the help of fear and repression, but it wasn't actually like that. Repression was felt by [jailed oligarch Mikhail] Khodorkovsky and a few other people. In fact, he just bought everyone off.

"Now the money is ending … so now he has turned to repression as a means of running the country."