The Phuket provincial court on Thursday found Lee Aldhouse guilty of stabbing to death ex-Marine Dashawn Longfellow after being beaten by the American during a brawl at a Phuket bar.
The court reduced Aldhouse's sentence from a life sentence because he pleaded guilty.
Aldhouse was a semi-professional kickboxer who fought under the nickname ``Pitbull.'' He had been living on-and-off in Phuket, where Longfellow was also studying the sport.
Aldhouse was extradited to Thailand last year in the first case of extradition of a criminal suspect from England to Thailand.
He was arrested at London's Heathrow Airport after fleeing Thailand.
Associated Press