Gleb Yakunin denounced the persecution of believers and spent several years in prison in the 1980s for speaking out against the Soviet state.
He also accused top Church officials of been in collaboration with the KGB in Russia.
When he stood for the post-Soviet Russian parliament he was defrocked but was also elected and served two years.
He was excommunicated in the late 90s for reasons still unknown.
He's survived by his wife and three children.