Phrathep Visuthikavee, head of the Buddhism Protection Center of Thailand, has been petitioning for the religion to be officially recognised in the constitution for years.
He says he now has more than a million signatures of support.
"If we all believe the constitution is the highest law in the country, what appears in the law should be the highest too," he told Al Jazeera.
"We put the matter of the country and the king in the law, so we must put the matter of religion too."
Critics fear enflaming tensions in the
already troubled south [AFP]
But many others fear such a move risks enflaming ongoing violence in Thailand's Muslim-majority south.
The committee responsible for drafting the new constitution is divided on the issue.
No previous constitution has ever declared a national religion, although by law the king must be Buddhist.
Dr Mettanando Bhikkhu, an advisor to the United Nations on Buddhist affairs, says he is convinced that declaring a national faith would worsen tensions in the south where Buddhists and Muslims are already deeply suspicious of each other.
"Once we nationalise the status of Buddhism it becomes aggressive," he says.
"Every time when Buddhism is married with nationalism, the offspring is always a demon."