Russia's Supreme Court designated the Christian denomination as "extremist" in 2017, liquidating and banning its nearly 400 chapters across the country.
Russia counted roughly 175,000 active believers at the time of the ban, according to the group's Russian website. Since then, raids, interrogations and jailings of adherents have occurred with some regularity.
The case against Aleksandr Chagan, 52, was built around a "mole" who secretly filmed worship meetings held by videoconference, said the spokesman, Jarrod Lopes.
Sentenced by a court in Tolyatti on Thursday, Chagan is the sixth Witness to receive eight years, the longest term imposed since the ban, Lopes said.
Religious life in Russia is dominated by the Russian Orthodox Church, which is championed by and loyal to President Vladimir Putin. Some Orthodox scholars view Jehovah's Witnesses, known for door-to-door preaching and refusing military service, as a "totalitarian sect".
At least 794 Witnesses have been criminally charged in Russia for their faith, and 127 are currently serving prison sentences, Lopes said.
Last month, four Witnesses in the same Russian region were handed seven-year jail terms in Samara, the same region as Chagan, while a female believer was sentenced in Tolyatti to two years' forced labour.
The European Court of Human Rights, the court of the Council of Europe, ruled in June 2022 that the ban was illegal, three months after the Council expelled Russia over its full-scale invasion of Ukraine.
(Reporting and writing by Lucy Papachristou; Editing by Kevin Liffey)
