Voters will be asked whether they accept the draft constitution, and whether to permit the country's Senate to jointly vote for Prime Minister along with the House of Representatives.
Feelings were mixed among Bangkok residents as voting progressed peacefully throughout the capital.
Some see the document as the legitimization of the military's rule, rather than part of a road back to full democracy, as Prime Minister Prayut Chan-o-cha, former commander in chief of the Thai army, claims.
Chaiwat Rattanawitthayapol, a 46-year-old businessman, told CNN after he casted his vote that he chose not to accept this draft constitution because it was written by the regime and he could not bear to see an appointed -- as opposed to elected -- prime minister continue to run the country.
"I can't accept it. It is the military's constitution -- they would just want to write it in the way to maintain their power," he said.
Jirattha Vitthaya, a 40-year-old company worker, said she voted against the new draft.
"This constitution is not from the people ... (those) who wrote it were selected by the military," she said.
"They said it is for the sake of the country, but how can only a (small) group of people say this is for the whole country?"
Others looked at the relative calm that military rule has brought to the country as reason enough to vote in the suggested changes.
Im Jeepetch, 18, a first-time voter, admitted she didn't know much about the draft constitution but voted "yes" because she feels that Bangkok has become more orderly and peaceful since the military came to power.
The calm in the city has made it easier for her to travel to her school, the university student said.
Results are expected late Sunday evening local time. If passed, it will be Thailand's 20th constitution.
Prayut has said that he will personally vote in favor of the constitution.
However, many Thais and international observers are skeptical of those claims, as the new constitution will cement military rule throughout the country's governmental institutions.
Among the sweeping changes introduced, the document will allow for the Prime Minister to be appointed by the National Assembly, rather than elected, and reserves seats in the Senate for the military.
The drafting process which led to the document being voted on was also heavily dominated by the military, and discussion or criticism of the new constitution was muzzled.
"The junta's use of its draconian sedition law against critics of the draft constitution creates a climate of fear ahead of the referendum," Brad Adams, Asia director of Human Rights Watch, said in a statement
"Military repression has become a daily reality in Thailand, and it's intensifying as the August 7 vote approaches."
Analysts say the constitution will allow the military to maintain power in future without the need to stage coups, of which Thailand has seen 12 since 1932.
"The draft constitution aims to entrench the power of the military and traditional elite, and if it passes the referendum Thailand will move toward semi-authoritarianism guided by the military," according
to the Institute of Southeast Asian Studies, a Singapore-based research organization.
"With the army's power embedded in the constitution, backed by the Constitutional Court's "state of exception" powers, the traditional elites would in effect have designed new mechanisms to seize power without resorting to a military coup."