Gen. Sondhi Boonyaratkalin said he would act as prime minister until the Council of Administrative Reform selected a new one, and an interim constitution would be drafted during that time, reported the Associated Press.
He said Thailand's foreign policy and international agreements would remain unchanged.
King Bhumibol Adulyadej, who supported the coup, appointed Sondhi as head of the council.
The military said the coup -- Thailand's first in 15 years -- was necessary to bring the country out of a protracted political crisis, according to Reuters.
The takeover occurred while Prime Minister Thaksin Shinawatra was attending U.N. meetings in New York. Thaksin is accused of corruption and undermining democratic institutions.
Thaksin flew to London on Wednesday but reportedly had no meetings scheduled with British Prime Minister Tony Blair.
The European Union condemned the military takeover and Washington expressed concern, the AP reported.
The U.S. State Department issued a statement saying it hoped "the Thai people will resolve their political differences in accord with democratic principles and the rule of law."
Australian Prime Minister John Howard called the coup a "great disappointment."
Japan also called for a quick restoration of democracy in a country where many of its businesses have factories and affiliates, according to the AP.
China, however, said the coup was "an internal affair of Thailand" and made no public judgment.