The 65-year-old ex-army chief led the 2014 coup, the last of at least a dozen since 1932 by a military woven deeply into the country's turbulent politics
Junta chief Prayut Chan-O-Cha formally became Thailand's 29th prime minister Tuesday after a royal endorsement, completing a long transformation from soldier to civilian leader and vowing "love, unity and compassion."
But critics may doubt the divisive leader's pledge after his previous stint in power which was marked by a ban on political gatherings, a clamp down on the media and the muzzling of dissent.
The 65-year-old ex-army chief led the 2014 coup, the last of at least a dozen since 1932 by a military woven deeply into the country's turbulent politics.
Thailand's first parliament since the coup was stacked with 250 hand-picked senators who helped vote Prayut in as prime minister over the charismatic and embattled leader of the Future Forward party.
But he holds a razor-thin majority in the lower house in a country frustrated by the military's influence on politics, with the hashtag #RIPThailand trending on Twitter after the vote.
"I will promote a peaceful environment for a unified society based on love, unity and compassion," Prayut said after the royal decree was read out at Government House.
He also promised to "listen to the voices of the people" and protect the monarchy.
Moments before his remarks he knelt before a portrait of King Maha Vajiralongkorn, clasping his hands together in a wai and bowing several times.
Prayut faces a rocky transition trailed by questions of legitimacy.
His challenger in the vote was billionaire and auto parts scion Thanathorn Juangroongruangkit, who has captured millenial hearts with his slick social media presence and withering anti-junta salvos.
The party scooped up 81 seats to become the third largest in Thailand.
But analysts say Thanathorn's magnetic appeal has made him and the party a target.
The Future Forward leader and his deputies are facing more than a dozen legal complaints that they say are politically motivated.
Thanathorn was suspended from parliament while one of the cases plays out and could face a ban from politics and jail time if convicted.
He was unable to attend the vote for prime minister even though he was the only other candidate.
Police are also probing a complaint against party spokeswoman Pannika Wanich for allegedly breaching the country's royal defamation law. She denies the claim.
Observers say Future Forward offered a fresh alternative for voters tired of familiar political camps.
For the past 13 years Thailand has been rocked by violent protests and takeovers in a broad split between supporters of the powerful Shinawatra clan and an arch-royalist elite backed by the military.
Yingluck Shinawatra's administration was toppled in the 2014 coup and her brother Thaksin was ousted by the military in 2006.
Both siblings live in self-exile but their main political machine Pheu Thai backed Thanathorn as candidate for prime minister.