The former army chief’s party lost May’s election to a party challenging the royalist military establishment.

His announcement on Tuesday followed the heavy defeat of his military-backed United Thai Nation party in the May 14 election, which won just 36 of the 500 house seats. An upstart movement of young monarchy critics, led by the progressive Move Forward Party, was the single biggest winner in the election.

Prayuth will remain the caretaker premier until a new government is formed.

Prayuth and controversies

The former army chief, a staunch royalist, led a military government until an election in 2019 and was chosen by parliament to remain prime minister for four more years.

In the nine years since his coup, Prayuth has survived multiple challenges via court cases, house confidence votes and street protests by opponents who saw him as an opportunist who lacked a public mandate.

His opponents have long claimed the 2019 election result was predetermined, which Prayuth, 69, has denied.

Prayuth said in a statement on Tuesday that he had “achieved many successes” during his time in power.

“I as prime minister have worked hard to protect the nation, religion, monarchy for the benefit of the beloved people. The result is currently bearing fruit for the public,” he said.

“I have tried to strengthen the country in all areas for stability and peace and overcame many obstacles domestically and internationally.”

His announcement comes as the new parliament prepares to convene on Thursday to vote on who will be the next prime minister, an outcome far from certain.

‘Lese majeste’ law in the spotlight

The monarchy’s role in Thailand has been at the centre of the political debate in Thailand as reformers look to dislodge the grip on power of the royalist military establishment.

The Move Forward Party, led by Pita Limjaroenrat, 42, achieved a stunning victory with its allies in the May election. Still, reforms aimed at the monarchy could stand in the way of Pita becoming prime minister.

One such reform is Move Forward’s proposal to amend the “lese majeste” law, Article 112 of the criminal code, that punishes insulting the monarchy with up to 15 years in prison.

In a country where reverence for the monarch has been promoted as central to national identity for decades, the idea is so radical that minority parties and many members of the appointed Senate have promised to block Pita from becoming premier.