Since leading a coup to oust Yingluck Shinawatra and installing himself as the country's prime minister in 2014, Prayuth has repeatedly assured foreign leaders and visiting dignitaries of the junta's commitment to democratic transition through free and fair elections.
"In November 2018, there will be an election".
Last year, the military pushed through a new constitution that critics said would boost military power and limit the sway of elected officials.
"Around June we will announce the [exact] date for the next election", Prayuth told reporters at Bangkok's Government House.
The Thai military has seized power 12 times since 1932, but earlier this year pledged not to stage another coup after the next election.
The prime minister also said the junta was considering whether to allow political activity - which it suspended after taking office - to resume after funeral services later this month for King Bhumibol Adulyadej, who died a year ago.
"Prayuth wants to delay the election but he knows that after the king's cremation, there will be pressure for an election", said Kan Yuenyong of the Siam Intelligence Unit think tank.
Years of competing protests and instability followed.
Thailand's main stock index rose 0.7 per cent after the news, having opened on Tuesday down 0.3 per cent.
He warned political parties against campaigning and said any breaches could result in the ban on political activities being prolonged.
The coup that overthrew Yingluck Shinawatra capped a decade-long period of political turmoil that began when her brother, former Prime Minister Thaksin Shinawatra, was himself forced out of office in 2006 by the military, which backed Thailand's Bangkok-based royalist-leaning, wealthy elite.
Thaksin's governments, or those backed by him, have won every election since 2001, partly due to their overwhelming popularity with politically-powerful rural voters.