Prayut, 69, is running with the new United Thai Nation Party, and will likely face Pheu Thai party's Paetongtarn Shinawatra, daughter and niece of two former premiers from the billionaire family, at the May 14 election.

The incumbent, in power since 2014 when the military toppled a civilian government, was elected as a civilian leader in 2019.

The military veteran has lagged behind rivals in opinion polls but hopes to win over supporters with promises to look after the well-being of the people and the country's stability and protect the monarchy.

"We volunteer to make everyone as happy as possible," Prayut said at a party event to introduce its candidates for all 400 constituencies.

He said his next government would continue the work of his current administration with a steady hand and the slogan: "Have done, doing and will continue."

"The most important thing is to defend the country and protect the nation's main institution. Please trust me as you've always done," Prayut said.

Party leader Pirapan Salirathavibhaga was nominated as the party's No. 2 candidate for prime minister.

Thailand's election is set to be a showdown between elite establishment and pro-democracy forces that have dominated politics in the South East Asian country for decades.

Australian Associated Press