David Taylor, 34, had admitted getting into the fatal fight with officer Wayan Sudarsa, but denied killing him.
His girlfriend, Australian national Sara Connor, 46, was sentenced to four years for her part in the murder.
The mother-of-two had maintained her innocence, insisting she only intended to pull the two men apart as they fought.
Both were arrested last August, after the traffic policeman was found beaten to death on a popular tourist beach.
The fight had broken out when Taylor had accused Mr Sudarsa of stealing his girlfriend's handbag, resulting in Taylor hitting the officer with items including binoculars and a beer bottle.
Mr Sudarsa's blood-soaked body was later found on Kuta beach with dozens of wounds on his neck, chest and head.
During the trial, which lasted four months, Taylor had claimed he was acting in self defence and was "in fear of his life".
However the judge told the court he had been "legitimately and convincingly proven guilty" of group assault causing death.
The pair, who were tried separately, were both found guilty of "group assault causing death", but were not convicted of the more serious charge of murder brought against them as prosecutors recognised that they did not intend to kill the officer.
A murder conviction would have carried a maximum jail term of 15 years.
The couple, who were based in Australia, had fled from the scene following the fight, but were tracked down when Connor's driving licence and bank card were found next to the body.