Prime Minister Prayut Chan-o-cha said he would vote on Sunday to accept the draft charter and to allow senators to join MPs in electing a prime minister.
He also insisted once again that a general election would take place next year regardless of the outcome of the referendum.
The general stressed he had no plan to prolong power but the country would need stability at least over the next five years for reform and development to take hold.
Gen Prayut made the statement during a ceremony to mark the 129th anniversary of the Chulachomklao Royal Military Academy in Nakhon Nayok province on Friday.
The prime minister apparently intended to let the public know how he would vote, as he had his close aide advise reporters to ask him the question.
"This is my personal standpoint. I think I can also speak out as many others have done so," the prime minister said.
It would be useless to vote yes to only one of the two questions at the referendum, he added.
Voters will be asked two questions on Sunday. One is whether they accept the draft constitution. The other question is long and complex but essentially asks whether they allow junta-appointed senators to vote with MPs to elect a prime minister in the first five years after the charter takes effect.
According to the referendum law, a voter may choose to vote only one of the two questions without invalidating a ballot but the prime minister doesn't recommend it.
"Choosing only one of them won't make a difference. Everything will go back to square one," Gen Prayut said.
The country learned its lesson and needed change as well as proper constitution and government to develop it in the way that the majority of people wanted, he said.
"As the chief of the NCPO (National Council for Peace and Order), I would like to say that we are here to improve national order and create stability to let the country develop the kind of democracy that meets international standards," Gen Prayut said.
He denied his government wanted to prolong its power but said that the country would need stability for at least another five years to facilitate the implementation of national strategies, development schemes and reform plans.
"The government does not want to prolong its power. I keep saying that we must have an election in 2017 because it is the promise made with local and international parties," Gen Prayut said.
"If I were a dictator as many people said, I would not have to have the referendum or announce the election in 2017," he said.