Mr. Navalny had won rulings against the Russian government over the same seven arrests in February 2017, when the court decided they were arbitrary, that he had not received fair trails and that his right to assembly had been violated.
The appeal handed him an additional victory for two of the seven arrests under an article that prohibits ulterior motives in prosecutions, including political motives, and that has an extraordinarily high bar of proof, lawyers who have litigated at the court said.
“My sense is the European Court of Human Rights has really done its job,” said Grigory V. Vaypan, a lawyer at the Institute of Law and Public Policy in Moscow. “For many people in Russia, the prosecutions of Navalny have looked political from the outset.”
The ruling comes at a tense moment, as Moscow, angry over previous rulings, has already threatened to withdraw from the court’s jurisdiction, ending a post-Cold War effort to integrate Russia into the Continent’s human rights architecture.
A judgment under the rule, Article 18, “essentially accuses the member state of lying” about the reasons for prosecutorial action, Jeffrey D. Kahn, a law professor at Southern Methodist University in Dallas and an authority on the European Court of Human Rights, said by telephone.
“That’s a pretty monumental decision,” he said, particularly as it was accompanied by an order to loosen laws on public assembly.
Russia has more cases before the court than any other country. In October, 10,950 allegations of rights abuse were pending against the Russian government, about 19 percent of the total docket. Russia has stopped paying dues for the court’s operations, and senior Russian officials say the country may soon sever ties.
“Europe is not only facing Brexit, one country leaving the European Union, but at the same time may also see a Ruxit, that Russia is leaving the European Convention on Human Rights,” Thorbjorn Jagland, the secretary general of the Council of Europe, said this month. “It will be a different Europe, and I don’t see any good things coming out of it.”