The ruling came hours after another judge rejected the top Kremlin critic's appeal over his prison sentence for violating the terms of his probation.
Mr Navalnysaid he had no regrets about returning to Russian Federation, that his belief in God helped sustain him, and that "strength was in truth".
Russian investigators said Navalny's tweet "denigrated the honor and dignity" of 95-year-old war veteran Ignat Artemenko, who was among the athletes and celebrities that appeared in the video.
Navalnywas arrested last month upon returning from Germany following treatment for poisoning with what many Western countries say was a military-grade nerve agent.
Late last month, Secretary of State Antony Blinken called on the Russian government to release Navalny, and in a ruling on Tuesday, the European Court of Human Rights followed suit, citing "the nature and extent of risk to the applicant's life".
Tens of thousands of protesters took to the streets of Moscow, St. Petersburg and across Russian Federation to demand the release of prominent Kremlin critic Alexei Navalny this past weekend.
Navalny was accused of defaming a World War II veteran who appeared in a video previous year advocating removing presidential term limits, which would allow Putin to stay in power beyond 2024. Authorities responded with a sweeping crackdown, detaining about 11,000 people, many of whom were fined or given jail terms ranging from seven to 15 days.
"I don't want to show off a lot, but the whole world knew where I was", Navalny said.
On February 16, the European court of human rights (ECHR) ruled that Russian Federation risked breaching the European Convention on Human Rights if it did not release Navalny immediately, according to Bloomberg.
Navalny said he was an atheist before but has come to believe in God, adding that his faith helped him face his challenges.
Asked about the impact of Navalny's prison sentence on Russia's politics, Kremlin spokesman Dmitry Peskov told reporters that the country's "rich and multifaceted" political scene will develop regardless of the verdict.
A law enforcement officer walks with a dog near a court building during a hearing on Alexei Navalny's appeal of his sentence in Moscow on Saturday.
European Union member Lithuania's foreign ministry said Friday that a group of European Union foreign ministers will meet with two top Navalny aides in Brussels on Sunday. "They want the righteousness and sooner or later they will have it".
The Russian government has rebuffed the Strasbourg-based court's demand, describing the ruling as unlawful and "inadmissible" meddling in Russia's affairs.
But he has said his comments were not specifically directed against the veteran, and that the authorities are using the charge to smear his reputation.
Later on Saturday, Navalny also faced proceedings in a separate case on charges of defaming a World War II veteran. Navalny is best known for his anti-corruption investigations and was recently the subject of an assassination attempt.