Thomas Mayo made the prediction on the coming referendum as he made the case for the 'yes' vote alongside several advocates and legal experts in Sydney on Wednesday evening.
"There is a great majority of Aboriginal and Torres Strait Islander people who are going to be voting yes," he said.
"And they want you to vote yes with us."
Mr Mayo, a member of the government's referendum working group, said he knew that was how Indigenous people would vote due to how the voice was conceived in a 2017 convention of First Nations leaders at Uluru.
The convention was comprehensive, well-informed, well-formulated and in his view, repeatable.
"If you ran that process again with 10 times the people and 10 times the resources, you'd get the same result," he said.
"Our people want to be heard.
"We have the solutions.
"We want the parliament to act on what we say."
Australians will be asked later this year whether they support an Indigenous advisory body being enshrined in the constitution.
To succeed, the 'yes' case requires support from a majority of the population and four of the six states.
Constitutional reform expert Shireen Morris reminded the audience of the lack of Indigenous people in the room when the nation's founding document was authored in the 1890s.
That resulted in a top-down dynamic from government, even after the discriminatory policies of yesteryear were removed, she said.
"The only way to fix that top-down dynamic is by guaranteeing that Indigenous people will always have a voice," Dr Morris said.
Campaigning for the referendum, expected between October and December, has escalated this week after both the 'yes' and 'no' camps revealed the arguments they will make to win voters to their respective sides.
Retired sporting stars Evonne Goolagong Cawley, Eddie Betts and Johnathan Thurston are featured in the 'yes' document.
Lawyer and land rights activist Noel Pearson stressed the voice was a way to recognise the nation's Indigenous heritage, which he described as the "unfinished work of the Australian project".
Indigenous Australians Minister Linda Burney said the voice would give communities the power to be heard.
"Unlike government, it will not be distracted by three-year election cycles," the Labor MP said.
Ms Burney earlier dismissed an invitation to debate prominent 'no' campaigner, opposition Indigenous spokeswoman Jacinta Nampijinpa Price.
Ms Price says instead of getting details, consultation and transparency, she and her colleagues had been given a rushed process.
The voice proposal was risky, full of unknowns and would add division to the constitution, she said this week.
Wednesday's forum in Sydney Town Hall acted as a 'yes' campaign event and marked journalist Stan Grant's return to the public arena.
He stepped away from his ABC commitments eight weeks ago, citing the toll of racist abuse.
It also officially began the City of Sydney's 'yes' campaign - five years after the council supported the Uluru Statement from the Heart.
Lord Mayor Clover Moore pointed to the success of its own 'voice' - an advisory panel established in 2008 that she said gave Aboriginal and Torres Strait Islander people "ownership, responsibility and accountability".
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