The man, identified only as Robert M. under Polish privacy laws, was one of four individuals who appeared before the judge at the regional court in the northwestern city of Szczecin on Monday, Poland's PAP news agency reported.
A fifth member of the group, Zbigniew B., thought to be the actual killer, had died in 2017.
The verdict was based mainly on the damning testimony of another of the men, Rafał O., who revealed, after more than a decade, how the group killed and partly ate an unidentified man near Lake Osiek in Poland's western Lubuskie province in 2002, the PAP news agency reported.
According to Rafał O., sometime between July and October of that year, Robert M. got into an altercation with an unnamed individual outside a village bar. He then drove this person to Lake Osiek, accompanied by the rest of the group, and ordered Zbigniew B. to kill the captive.
Zbigniew B. duly slit the victim’s throat and beheaded him with a knife. The five men proceeded to profane the remains, by roasting parts of the victim’s body in a fire pit and eating them.
Szczecin’s regional court found Robert M. guilty of “masterminding the perpetration of a forbidden act,” the killing of the victim, and sentenced him to 25 years in prison, PAP reported.
The three other defendants were ruled guilty of “desecrating the victim’s corpse” by “dismembering his body, roasting the different parts and partly consuming them.”
The lawyer for Robert M. said she would lodge an appeal against the man's 25-year prison sentence, the Polish state news agency reported.