The former prime minister, who was ousted from the country's top job and more recently as a climate tsar in NSW, has given evidence to a Senate inquiry into media diversity on Monday.

"The most powerful political actor in Australia is not the Liberal Party or the National Party or the Labor Party, it is News Corporation," he said.

"And it is utterly unaccountable. It is controlled by an American family and their interests are no longer, if they ever were, coextensive with our own."

Mr Turnbull says he faced a ferocious campaign from News Corp after he was recently named as head of a climate advisory board for the NSW government.

The state government "crumbled" to that but then said it was not because of the media organisation, the former Liberal leader said.

"This is like somebody who is taken down to the police station, beaten over the head until they finally sign a fake confession, the last line of which says: 'I confirm that I did so of my own free will.'"

Mr Turnbull is concerned about the trend of narrowcasting in the news media, where information is being targeted for a niche audience.

"There is now a market for crazy," he said.

"If you doubt the significance of this, just reflect on the damage that Murdoch's publications and outlets particular in the United States have done to democracy there."

The one-time journalist pointed to the storming of the United States Capitol in early January, propelled by reports from Rupert Murdoch-owned media organisations the election had been stolen from former president Donald Trump, who had lost.

Mr Turnbull also criticised the organisation for promoting animosity towards Muslims and preventing effective action on climate change.

He blames News Corp and radio shock jocks for helping to fuel his demise.

"Being as candid as I have been today is something that you would do at your peril if you were prime minister or a minister or you wanted to keep staying in parliament, because the retribution would be very intense," he said.

"Even if you were prepared to take the heat, your colleagues definitely wouldn't."

Former Herald Sun editor and co-founder of The New Daily Bruce Guthrie said News Corp had a list of "friends and enemies" who were rewarded or punished.

Mr Guthrie said it was important for the government to help the Australian Associated Press news wire in order for news startups to succeed.

Mr Turnbull shared his sentiment.

"The survival of AAP as an independent news wire service is really important, because what it's doing is providing the bulk of the news copy for a lot of smaller publishers. Whether they're broadcast or print or just online."

Australian Associated Press