BANGKOK, Thailand — Thailand’s Constitutional Court on Wednesday removed Prime Minister Srettha Thavisin from office for an ethical violation after he appointed a convicted criminal to his cabinet, in a stunning decision that tosses the government into a scramble for leadership just a year after ending a decade of military-dominated control.

The move deepens a time of uncertainty for democratic rule in a key U.S. ally in the region, coming just a week after the same court ordered the dissolution of the main opposition party that captured the most votes in the country’s breakthrough national elections in the spring of 2023.

The sharply divided judges on Wednesday focused on Mr. Srettha’s appointment of Pichit Chuenban as a top aide. Mr. Pichit had been convicted of attempting to bribe a court official with thousands of dollars in a paper bag and was imprisoned for six months in 2008. The court said that although Mr. Pichit had already served his jail term, his behavior was dishonest.

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“I’m sorry that I’d be considered as a prime minister who is unethical, but that’s not who I am,” Mr. Srettha, a former leading business executive who has been in office just under a year, said after the court’s ruling.

Mr. Srettha’s selection of Mr. Pichit as minister to the prime minister in May sparked immediate criticism from opposition politicians and the press, and he was forced to quit the Cabinet just 19 days later.

The Constitutional Court’s final verdict also resulted in Mr. Srettha’s entire Cabinet of ministers transforming into temporary caretakers.

That change is expected to slam the economy because decisions about investment and other financial issues may be delayed until a new Cabinet is installed, according to analysts, although Bangkok’s foreign policy is unlikely to see major change in the short term.

After the court ruled 5-4 to disqualify Mr. Srettha, 62, for breaching “rules on ethics,” he was quickly replaced by caretaker Prime Minister Phumtham Wechayachai, the current commerce minister and a member of the PTP, until Parliament can convene on Friday to elect the next prime minister. It was not immediately known if he would contest for the top position.

Thailand’s complex and often opaque political system, including a Senate filled with supporters of the military, makes the next steps hard to predict. The current squabbling 11-party governing coalition could unite behind a single candidate or split into rival factions joining other parties, especially the increasingly powerful military-aligned cliques.

Mr. Srettha had jumped from his lucrative property marketing career into politics one year ago in August 2023, and helped to end Bangkok’s nine years of military-dominated governments. Many perceived him as a pliant puppet of controversial former Prime Minister Thaksin Shinawatra, whose family dominates the Pheu Thai (“For Thais”) Party.

“Whether the Pheu Thai Party (PTP) will have the [prime ministerial] slot will depend on discussions with coalition parties,” PTP Secretary-General Sorawong Thienthong told the Bangkok Post. “If other coalition parties propose candidates to be the next prime minister, we will be pleased.”

Just a week ago, the same Constitutional Court expelled from politics Thailand’s most popular opposition politician, Pita Limjaroenrat, plus 10 of his executives, and dissolved Mr. Pita’s Move Forward Party (MFP). Mr. Pita’s downfall resulted from him repeatedly demanding the king’s powerful legal protection against libel be weakened and “reformed” — still a taboo subject in this Buddhist-majority Southeast Asian U.S. military ally.

Mr. Pita and his now-disbanded MFP came in first place in May elections for parliament’s Lower House. They failed, however, to fashion a governing coalition in the face of opposition from lawmakers aligned with the military and the monarchy.

Military officers, royalists and other conservative forces appear to be gaining from the past week of judicial decisions, according to some analysts, despite their poor showing in the 2023 vote.

Many here see Thailand’s courts, especially the Constitutional Court, as an extension of the country’s royalist establishment, which has its recent rulings to undercut or oust political opponents.

The Constitutional Court’s rulings this month are “two judicial coups” that are “against international standards and upset the usual checks and balances in a democratic system,” Prajak Kongkirati, a political scientist at Bangkok’s Thammasat University, told The Associated Press.