Dennis Christensen gestures from inside a defendants' cage during a break in the reading of his verdict at a court in the town of Oryol on February 6, 2019.
With about 170,000 followers in Russian Federation and 8 million worldwide, Jehovah's Witnesses are a Christian denomination known for door-to-door preaching, close Bible study, and rejection of military service and blood transfusions.
The almost 622 days Mr Christensen has already spent in confinement will reportedly count for about half of the six-year sentence.
Human Rights Watch condemned the sentencing and verdict Wednesday.
Christensen spent 20 months in pretrial custody.
Amnesty International says that since Christensen's arrest more than 50 other Jehovah's Witnesses have been charged by the Russian state with violating anti-extremism legislation, with dozens in detention or under house arrest.
The religion was founded in Pennsylvania in the 1800s. "We agree with President Putin that persecuting peaceful believers is utter nonsense, and call on Russian Federation to respect freedom of religion".
His sentencing spurred condemnation from the worldwide community at a time when Russian Federation has been criticized for its crackdown on dissent.
Dennis Christensen was arrested in May 2017 after a police raid on his congregation just south of Moscow.
In 2010, the European Court of Human Rights ruled that the dissolution six years earlier of the movement's Moscow branch had violated the right to freedom of religion and association. Critics are concerned for religious freedom in the country. "It's shocking that in post-Soviet Russia authorities are putting people through the ordeal of a criminal investigation and prison for nothing more than peacefully practicing their faith".
According to Jehovah Witness spokesman in Russia Yaroslav Sivulskiy said the religious sect regretted the conviction of Christensen.
"It is sad that reading the Bible, preaching, and living a moral way of life is again a criminal offence in Russian Federation".