A Moscow court has ordered the Russian opposition leader to prison on charges that he violated the terms of his probation while he was recuperating in Germany from nerve-agent poisoning.
Mr Navalny had earlier denounced the proceedings as a vain attempt by the Kremlin to scare millions of Russians into submission.
The prison sentence stems from a 2014 embezzlement conviction that he has rejected as fabricated.
The 44-year-old was arrested on January 17 upon returning from his five-month convalescence in Germany from the attack, which he has blamed on the Kremlin.
Russian authorities deny any involvement despite tests by several European labs, that they have no proof he was poisoned.
As the order was read, Mr Navalny pointed to his wife Yulia in the courtroom and traced the outline of a heart on the glass cage where he was being held.
Earlier, Mr Navalny attributed his arrest to Mr Putin’s "fear and hatred" saying the Russian leader will go down in history as a "poisoner".
He said: "I have deeply offended him simply by surviving the assassination attempt that he ordered. The aim of that hearing is to scare a great number of people. You can’t jail the entire country."
Russia’s penitentiary service alleges that Mr Navalny violated the probation conditions of his suspended sentence from a 2014 money laundering conviction that he has rejected as politically motivated.
It asked the Simonovsky District Court to turn his three-and-a-half year suspended sentence into one that he must serve in prison, although he has spent some of that sentence under house arrest.
Mr Navalny emphasised that the European Court of Human Rights has ruled that his 2014 conviction was unlawful and Russia paid him compensation in line with the ruling.
Mr Navalny and his lawyers have argued that while he was recovering in Germany from the poisoning, he could not register with Russian authorities in person as required by his probation.
Mr Navalny also insisted that his due process rights were crudely violated during his arrest and described his jailing as a travesty of justice.
He said at Tuesday’s hearing: "I came back to Moscow after I completed the course of treatment. What else could I have done?”
Mr Navalny’s jailing has triggered massive protests across Russia for the past two weekends, with tens of thousands taking to the streets to demand his release and chant slogans against Mr Putin.
Police detained more than 5,750 people on Sunday, including more than 1,900 in Moscow, the biggest number the nation has seen since Soviet times.
Most were released after being handed a court summons, and they face fines or jail terms of seven to 15 days. Several people faced criminal charges over alleged violence against police.
Mr Navalny said: "I am fighting and will keep doing it even though I am now in the hands of people who love to put chemical weapons everywhere and no-one would give three kopecks for my life."
Mr Navalny’s team called for another demonstration outside the Moscow courthouse, but police were out in force, cordoning off the nearby streets and making random arrests.
More than 320 people were detained, according to the OVD-Info group that monitors arrests.