Thailand's Constitutional Court on Wednesday dismissed Prime Minister Srettha Thavisin for appointing to his cabinet a former lawyer who served jail time, raising the spectre of more political upheaval and a reset of the governing alliance.

"I respect the verdict. I reiterate that for the almost one year I have been in this role, I have tried with good intentions to lead the country with honesty," Srettha told reporters outside his office after the court ruling.

Real estate tycoon Srettha becomes the fourth Thai premier in 16 years to be removed by verdicts by the same court, after it ruled he violated the constitution by appointing a minister who did not meet ethical standards.

Srettha's removal after less than a year in power means parliament must convene to choose a new premier, with the prospect of more uncertainty in a country dogged for two decades by coups and court rulings that have brought down multiple governments and political parties.

The same court last week dissolved the anti-establishment Move Forward Party, the hugely popular opposition, ruling its campaign to reform a law against insulting the crown risked undermining the constitutional monarchy. It regrouped on Friday under a new party.

Srettha's Pheu Thai Party and its predecessors have borne the brunt of Thailand's turmoil, with two of its governments removed by coups in a long-running grudge match between the party's founders, the billionaire Shinawatra family, and their rivals in the conservative establishment and royalist military.

The decision could rock a fragile truce between political heavyweight Thaksin Shinawatra and his enemies among the conservative elite and military old guard, which enabled the tycoon's return from 15 years of self-exile in 2023 and ally Srettha to become premier the same day.

Srettha had maintained his appointment of former Shinawatra lawyer Pichit Chuenban, who was briefly imprisoned for contempt of court in 2008 over an alleged attempt to bribe court staff, was above board. The bribery allegation was never proven and Pichit resigned in May.

Deputy premier Phumtham Wechayachai is expected to take over as caretaker prime minister. (Agencies)