Slobodan Davidovic, a former member of the Serbian paramilitary unit known as "The Scorpions", was found guilty of participating in the killing of the six Muslim males from Bosnia's wartime enclave of Srebrenica.
"The accused actively participated in the whole operation from the moment he recieved an order from commander Slobodan Medic" to carry out the murders, said Judge Miroslav Sovanj, as quoted by Croatia's state-run HINA news agency.
Scorpions commander Medic is among five former Serb paramilitaries charged by Serbia's special war crimes court with murdering the six Muslims from Srebrenica in a case that emerged after a video of the shootings surfaced.
Their trial opened in Belgrade last week.
Davidovic's sentence included a nine-year term for torturing Croatian prisoners in the eastern village of Bobota, which was under the control of Serb rebels at the outbreak of the 1991-1995 Serbo-Croatian war.
The 52-year-old was arrested in the eastern Croatian village of Banovci in June this year after he was allegedly identified in the video footage.