The workers, Zaw Lin and Win Zaw Htun, were sentenced to death for the murder of David Miller, 24 and the murder and rape of Hannah Witheridge, 23, on the diving haven of Koh Tao.
Police said Witheridge had been raped and bludgeoned to death and Miller had suffered blows to his head.
A panel of two Supreme Court judges ruled on Thursday to uphold the death sentences handed down by lower courts, saying the men had been found guilty of murder and rape on the basis of evidence and forensic results.
The men displayed no emotion as they listened intently to a translator while the verdict was read at a court in the province of Nonthaburi, just north of Bangkok, the capital.
“Zaw Lin and Win Zaw Htun said afterwards that they were sad and worried by the verdict because they said they did not commit the crime,’’ the court translator, Aye Mar Cho, said.
Their lawyer said they would seek a pardon from Thailand’s king.
“We will petition for royal pardon within 60 days so they would not be executed,’’ the lawyer, Nakhon Chompuchart, said.
Thai law grants those sentenced to death 60 days to seek such a pardon, but if the king dismisses the request an execution can go ahead.
A murder convict was executed in June 2018 by lethal injection, but for the previous nine years all death sentences had been commuted by royal pardon.
Zaw Lin and Win Zaw Htun were convicted and sentenced to death in 2015, a verdict upheld by the appeal court in 2017.
A pro-bono legal team defending the men has said evidence collected by police was substandard.
The lawyers have also said they were tortured and coerced into making confessions they later retracted.
“DNA and forensic evidence was, in my opinion, fundamentally flawed and should always have been considered unreliable, when considered against international standards,’’ said labour activist, Andy Hall.
The Supreme Court on Thursday rejected accusations of torture and ruled that DNA evidence linked the workers to the crime. (Reuters/)