Mr Navalny, 44, said a court ruling from a police station was a mockery, urging people to stage street protests.
He was held soon after his flight from Germany landed in Moscow on Sunday.
Russian prosecutors say he violated the parole terms of a suspended sentence for embezzlement.
Mr Navalny has described the embezzlement charges as politically motivated.
US and European leaders have led calls for his release.
Mr Navalny was almost killed in an attack involving the nerve agent Novichok last August, which he blamed on the Kremlin. Moscow has denied involvement. The opposition politician’s allegations have however been backed up by reports from investigative journalists.
A court hearing was organised on Monday at a police station in Khimki, on the outskirts of Moscow, where Mr Navalny had spent the night.
The judge ordered Mr Navalny’s detention until 15 February for violating his parole. He will have another hearing on 29 January to determine whether his suspended sentence of three-and-a-half years should be replaced with a jail term.
Mr Navalny said his treatment was beyond a “mockery of justice” and described the hearing as “lawlessness of the highest grade”.
“Don’t be afraid. Take to the streets, not for me, but for yourselves, for your future,” he said in a video address (in Russian) from the police station.
Dozens of Navalny supporters gathered outside the police station in freezing weather, demanding his immediate release.
The US and European Union led calls for Mr Navalny to be freed, but stopped short of threatening any punitive action.
US Secretary of State Mike Pompeo said Russian authorities were trying to silence their critics, while incoming national security adviser Jake Sullivan said the Kremlin’s “attacks on Mr Navalny are not just a violation of human rights, but an affront to the Russian people who want their voices heard”.
France, Italy, Germany and the president of the European Commission were also among those calling for his release.
UK Foreign Secretary Dominic Raab described Mr Navalny’s arrest as “appalling”.
“Rather than persecuting Mr Navalny, Russia should explain how a chemical weapon came to be used on Russian soil,” he said.
Source: BBC