He gave the reaffirmation after the draft constitution, which has been unveiled by the drafting panel, met with strong criticisms, leading to speculation that it might be killed in a referendum.
Prayut said the general election would definitely take place next year but he declined to say which month.
The prime minister refused to say whether the roadmap would be affected because of the time taken to write organic laws, adding he did not know how many there were and whether drafters could speed up work.
Government spokesman Sansern Kaewkamnerd said last week that the Cabinet would also discuss the constitutional matter in their weekly meeting Tuesday.