Sarayud said that general elections would be held by the end of the year to restore democracy after last year's military coup which forced Thaksin Shinawatra, the twice-elected prime minister, from power.
"I reaffirm that the election will be held late this year," he said.
"The exact date is still under consideration, but I believe the most suitable date is after the king's birthday [December 5]."
The 186-page charter curbs the role of politicians, emphasises checks and balances at the expense of participatory democracy, and could perpetuate the power of the Thai military.
And critics say the new constitution, although steering the country out of direct military control, would prove a setback for democracy.
Sunday's partial tally showed that more than 40 per cent rejected the military-backed constitution, sending a signal to the generals who removed Thaksin that he remains a political force.
|"By voting 'yes', Thai people sent a clear message to the junta that they want elections in December" |
Members of his now banned Thai Rak Thai (TRT) said they accepted defeat, despite the full result of the vote not being returned.
"We accept the result of the referendum, and the promulgation of this constitution," Chaturon Chaisang, a former leader of the TRT, said.
Chaisang said the TRT did not support the constitution, and the referendum "was not conducted in a way that meets democratic standards."
"Government officials have misled the people by telling them there would be no elections if the constitution did not pass. They restricted the freedom of expression of people in the areas under martial law," he said.
Half the country has been under martial law since the coup, while a new law threatened prison for anyone convicted of obstructing the referendum.
The new charter will be Thailand's 18th constitution in 75 years of on-off democracy.
Vote for 'normalcy'
"By voting 'yes', Thai people sent a clear message to the junta that they want elections in December," Panitan Wattanayagorn from Chulalongkorn University said.
"They wanted to make sure to [tell] the coup group that they wanted democratic elections and they wanted the situation to return to normalcy soon," he said.
Many voters appeared to ignore the contents of the draft charter, focusing instead on either the election or the coup-makers.
"I haven't read the constitution but I think it's time to move on. It's time for an election. We can't eat the constitution," said Ammara Limmahakhun, in Chiang Mai, Thaksin's hometown in northern Thailand.
Opponents of the charter said it would limit the powers of elected leaders and roll back reforms included in the previous 1997 charter, setting the stage for fragile coalition governments that will be largely under the control of the military.
If it had been rejected by voters, the government could have imposed one of Thailand's 17 previous charters and amend it as they pleased.
A full official result is expected on Monday.