“For a lot of the middle class, especially upper-middle class Thais, he’s like the ideal son-in law that you’d like to have — very educated, accomplished, good-looking, poised,” said Duncan McCargo, a political science professor at the University of Copenhagen.

Mr. Pita was drawn to the ideas of the founder of the Future Forward party, Thanathorn Juangroongruangkit, in 2018, and within a few months was asked to join. He became the leader of Move Forward after Thailand’s Constitutional Court dissolved Future Forward in 2020 and barred its senior executives from politics for 10 years.

If his bid for prime minister is successful, Mr. Pita has promised to reset Thailand’s foreign policy, saying the country would “not be part of the Chinese umbrella or the American umbrella,” but will have the ability to determine its own destiny, Mr. Pita said. In March 2022, after Moscow invaded Ukraine, he wrote on Twitter that the Russians must “retrieve” their troops immediately.

“A lot of it is personal,” said Fuadi Pitsuwan, a fellow at Chiang Mai University and foreign policy adviser to Mr. Pita, referring to the candidate’s strong reaction to the invasion. “He will be a foreign policy leader, which, in Thailand, is rare.”