Myanmar migrant workers Zaw Lin and Win Zaw Tun were sentenced to death for the rape and murder of Hannah Witheridge, 23, and the killing of David Miller, 24.
The victims’ battered bodies were found on a beach in the diving resort island of Koh Tao in September 2014.
Defence lawyers have said the evidence used to convict the two men were unreliable as authorities had mishandled DNA and did not allow independent analysis of the samples.
They also argued that confessions by the pair were obtained under duress.
Defence appeals were exhausted in August.
Many supporters of the two men argue that they had been framed and that they had initially confessed to the crimes under duress.
The police investigation and handling of crucial DNA evidence were also widely criticised.
The death sentences will be reduced to life imprisonment under a royal pardon, their lawyer Nakhon Chompuchat told Reuters, reports the Bangkok Post.
“The two are eligible under a section in the royal pardon decree to get their death sentences reduced to life imprisonment,” Mr Nakhon said.
“They will also have a chance to get their sentences reduced further on good behaviour.”
The decree published in the Royal Gazette on Friday said the pardons were granted to commemorate His Majesty the King’s birthday on July 28.
It was not immediately clear how many other prisoners were eligible for pardons or reduction of sentences under different criteria listed in the decree, the Bangkok Post noted.