Wayne Schneider, a 38-year-old Australian, was kidnapped in December 2015 by a gang of masked men from an apartment in Pattaya, an eastern Thai city known for its seedy nightlife and links to organised crime.
His body was found days later after investigators tracked a GPS device in a hired van used to carry out the kidnapping.
Fellow Australian Antonio Bagnato, 28, was convicted by a court in Pattaya on Tuesday and handed down a death sentence, a punishment that remains on the statute books in Thailand but is rarely carried out.
American national Tyler Gerard, 22, was convicted of being involved in the kidnap and given a reduced two-year sentence for cooperating with authorities.
Australia, which opposes the death penalty, said Bagnato now plans to appeal.
‘An Australian man has received a death sentence in Thailand on murder charges and he intends to lodge an appeal,’ a spokesperson for the Department of Foreign Affairs and Trade said on Wednesday.
‘We continue to provide all appropriate consular assistance to the man and his family,’ the statement added.
Schneider's death once more highlighted the foreign criminal elements that flock to Pattaya, a beachside resort with a pulsating red light district and no shortage or grizzly crimes.
Australian biker gangs and underworld figures have long had a presence in the city.
Regional law enforcement officials say Thailand is often used as place to secure and smuggle methamphetamine and heroin into Australia from the Golden Triangle, one of the world's largest drug producing regions comprising the porous border regions where China, Laos, Myanmar and Thailand meet.
Schneider was once on an Australian ‘most wanted’ list for the shooting of a bouncer in the knee outside a Sydney nightclub.
Bagnato was also a suspect in a 2014 Sydney murder.
Both moved to Thailand and chose to live in Pattaya, seemingly unmolested by local law enforcement.
Australia's ABC News, which followed the trial, said the two men were once business partners who fell out, though the precise motive for the murder remains unclear.
There is a shrine to Schneider at a bar in Pattaya run by the local Hells Angels chapter, ABC reported.
Three men involved in the kidnapping remain uncaptured.
Thailand rarely executes prisoners. The last death penalties were carried out in 2009 for two convicted drug traffickers.
