O’Brien, who won six Walkley Awards while working on ABC flagship programs including 7.30 and Four Corners, took aim at unnamed ‘no’ campaigners during a ‘yes’ campaign event in Sydney.

Australians will be asked later this year whether they support an Indigenous advisory body being enshrined in the constitution.

“I see lies being told and not properly challenged,” O’Brien said on Wednesday night.

“I ask myself if there is a strength to the ‘no’ campaign against this referendum, why do the people substantially behind that campaign feel the need to lie?

“What does that tell us about the authenticity of what is motivating them?

“These are questions that I believe should be dealt with in a transparent and strong way by media and I have not seen it.”

O’Brien did not name individuals but called out the actions of the conservative political lobby Advance Australia.

The group was exposed by Crikey and the Guardian for paying for social media advertising that claims the voice proposal was either too much or not enough, depending on the demographic targeted.

O’Brien has acted as an authoritative voice for the referendum proposal and co-authored a handbook on the topic with referendum working group member Thomas Mayo.

Mr Mayo urged attendees at the Sydney campaign event to start conversations with friends and family about why they were voting ‘yes’.

“I want you to do that in a respectful way, in a way that will listen to their views so that you can put the best position back to them about why they should support it,” the Kaurareg Aboriginal, Kalkalgal and Erubamle Torres Strait Islander man said.

He said he believed “a great majority” of Indigenous people would vote for change in the referendum, due in the last quarter of 2023.

Campaigning for the referendum – the country’s first this century – has escalated this week after both the ‘yes’ and ‘no’ camps revealed the arguments they will make to win voters.

Supporters of the voice argue the advisory body will be a committee of Aboriginal and Torres Strait Islander people who will advise the government on issues that affect them.

The parliament of the day will have the power to decide how the voice operates but, unlike previous Indigenous advisory bodies, cannot completely erase it.

Opponents of the proposal argue the voice goes beyond recognition, is “legally risky, with unknown consequences”, and is divisive.

“If you don’t know, vote no,” the essay reads.

The ‘yes’ case requires support from a majority of the population and majorities in four of the six states.