He was killed following a legal dispute over a debt of about 270 million baht.
Lee Ah Han, 54, had been involved in a legal dispute with another Malaysian national who reportedly owed him 35 million ringgit (about 270 million baht).
Lee was killed to wipe out the debt, police said.
On December 4, 2015, Lee and his wife were shot by a man using an automatic rifle while they were in their black Mercedes-Benz S300 on Kanchanawanit Road in Hat Yai district.
They had been trailed by three vehicles. Lee’s wife was injured but survived.
The three vehicles were driven by a group comprising one Malaysian man, four Thai men, and one Thai woman.
Three of the men, including the Malaysian national, and the woman plead innocent. All received the death penalty.
The shooter and his driver, both Thai, admitted their guilt and were sentenced to life in prison.
Thirty witnesses were questioned during the trial.
Provincial attorneys carefully reviewed the evidence and interviewed the witnesses because it was a high-profile, violent crime, said Kosolwat Inthujanyong, deputy spokesman of the Office of the Attorney General.
Kosolwat said that the pair who pleaded guilty initially said they were innocent.
After learning that their accomplices – who had hired them to murder Lee – were trying to blame the murder entirely on them they admitted their guilt, Kosolwat said.
Executions in Thailand are done by lethal injection.