Detlev Guenzel, 56, strangled and dismembered the 59-year-old at a small bed-and-breakfast run by Mr Guenzel in eastern Germany in 2013.
Guenzel was sentenced to eight-and-a-half years in jail.
Prosecutors could not confirm that he had actually eaten the victim, but some body parts were never found.
Lawyers representing the family of the murdered man - 59-year-old Polish-born Wojciech Stempniewicz - sought a 15-year sentence for Guenzel, the father of three adult children described by neighbours as affable, warm hearted and courteous.
Guenzel went on trial in August for killing Stempniewicz at his home, a bed-and-breakfast inn in the town of Hartmannsdorf-Reichenau in the Erz mountains near the border with the Czech Republic.
He was accused of cutting the body into small pieces and burying them in his garden, making a macabre home video in the process.
The pair met in October 2013 on a website for slaughter and cannibalism fantasies which described itself as the "#1 site for exotic meat" with more than 3,000 registered members, correspondents say.
Guenzel, who had served in the police for 30 years, retracted a confession he initially made to detectives soon after Stempniewicz's killing in which he said that he had cut his throat.
The defence argued that Stempniewicz had a death wish and had already hanged himself in Guenzel's cellar "S&M studio" before he took a knife, then an electric saw, to the gagged-and-bound man.
Investigators have been unable to determine the cause of death definitively because of the poor condition of the corpse.
They have, however, been able to ascertain that the pair had extensive contact online and by telephone before finally arranging their date on 4 November 2013.
The video Guenzel made was played during the trial, at one point showing him covered in blood while mutilating the corpse. "I never thought I would sink so low," he can be heard murmuring.
The defendant is reported to have broken down when the footage was shown, telling presiding judge Birgit Wiegand that he had made a mistake but was not a murderer.
The case has echoes of the 2001 murder of Bernd Juergen Brandes by Armin Meiwes in Rotenburg in western Germany.
Meiwes is serving a life sentence after killing and eating parts of his victim, who agreed to his death.
A former German policeman has been convicted of murdering a businessman he met on a website for cannibalism fetishists.