The policeman, Epaminondas Korkoneas, was found guilty by the court in Amfissa, Greece, over the fatal shooting of a teenage schoolboy, Alexis Grigoropoulos, while on night patrol in December 2008.
The panel of three judges handed down a sentence of life in prison for the 38-year-old officer. Korkoneas's patrol partner, Vassilios Saraliotis was found guilty of complicity in the crime, given a 10-year jail term. The defense pledged to appeal the sentences.
The defense argued that the incident had been a tragic accident which arose as the police fired warning shots to disperse youngsters hurling objects at them.
The boy's autopsy report even indicated that he had been hit by a bullet that ricocheted on to him, but lawyers for his family presented witness testimony claiming the policeman had taken aim and fired.
The teenager's death sparked major riots in Athens and other Greek cities, which lasted for two weeks and caused extensive damage to government buildings, private businesses and automobiles.
A far-left extremist group threatened to kill Korkoneas, prompting authorities to relocate the trial from Athens to Amfissa, 200 kilometers (124 miles) north of the capital.
Author: Gregg Benzow (dpa,AFP)
Editor: Chuck Penfold