Mamikhan Umarov, 43, who was granted political asylum in Austria in 2005 and known locally as Martin Beck, was found dead with gunshot wounds near Vienna on July 4th last year.
A former policeman in Chechnya, Umarov ran a video blog critical of Chechen leader Ramzan Kadyrov, and worked with Austrian intelligence.
His killer, who was identified only as a 48-year-old Chechen man, had the victim’s blood on his left shoe and traces of gunpowder on his hands when he was arrested, according to investigators.
The defendant had pleaded not guilty at the court in Korneuburg in northeast Austria and vowed to appeal when the verdict was delivered, according to the court spokesman.
No motive for the crime was established, with prosecutors suggesting it was either an arms deal gone wrong or a political murder.
Umarov had given testimony in other murder trials involving Chechens.
Chechnya is a predominantly Muslim part of Russia. Two wars in the 1990s triggered a wave of emigration, with many Chechens heading for western Europe.
But more Chechens have fled into exile in recent years because of disagreements with pro-Kremlin Kadyrov, who activists accuse of repeated rights violations.