He was the first person arrested under a 2017 ruling which outlawed the religious group, deeming them an "extremist organisation".
Authorities in 2017 amended an existing anti-extremism law to mention Jehovah's Witnesses specifically, ordering their dissolution in Russian Federation.
Al Jazeera's Rory Challands reports from Moscow.
A Danish citizen with a Russian residency permit, Christensen was arrested at a worship service in May 2017 by armed police in the western city of Orel.
A Jehovah's Witness member has been sentenced to six years in jail for extremism in Russian Federation, years after the religious group was outlawed in the country. He had unlocked the entrance to the building and delivered a sermon that day but he was not a staff member of the organization, according Human Rights Watch.
Jehovah's Witnesses have for several years come under pressure from the Russian state.
However, he was found guilty by the court on Wednesday, February 6 for organising a meeting of a banned group.
More than 100 criminal cases have been opened against Jehovah's Witnesses, with another 24 people in prison awaiting or on trial and a similar number under house arrest.
Dennis Christensen is escorted inside a courthouse following the verdict announcement.
In December, Putin vowed to look into the persecution of Jehovah's Witnesses, saying the labeling of religious communities as terrorist organizations was "complete nonsense".
Christensen's lawyer Anton Bogdanov said that he will likely file an appeal within 10 days after discussing the matter with his client.
Kremlin Spokesman Dmitry Peskov did not comment on the information on this case earlier on Wednesday, promising to specify the information and noting that religious views alone could not prompt the charges.
"We deeply regret the conviction of Dennis Christensen - an innocent man who did not commit any real crime", said Yaroslav Sivulskiy, representative of the European Association of Jehovah's Witnesses. "It is sad that reading the bible, preaching, and living a moral way of life is again a criminal offense in Russia", Sivulskiy said in a public statement on Wednesday.
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