And the former prime minister still sees politics as a worthy calling but says the political and media environments have become much more vicious, driven in part by social media.

Mr Turnbull's tell-all memoir, A Bigger Picture, published on Monday, offers frank character assessments of those around him during his stint in politics as well as some by his colleagues about otheres.

This includes a complaint to him from Finance Minister Mathias Cormann in 2017 that the government had a "Treasurer problem" regarding Scott Morrison's suspected leaking to media.

Senator Cormann has disputed his former boss' recollection of events but Mr Turnbull in reply quoted the date and time the message was sent.

"When you write a story, a memoir, invariably you have to talk about events that occurred, discussions that were had," Mr Turnbull told the National Press Club on Wednesday, in a video appearance.

His story was one in the public interest, he said.

"But we're talking about history now ... the Turnbull government is over and has been over for nearly two years now.

"We're talking about the past and it's important that the truth be told."

In the book, Mr Turnbull opens up about the deep depression he fell into after he lost the Liberal Party leadership in 2009, saying it ambushed him.

But since making that battle public, he says many people have thanked him for the openness.

"It's a shocking business, depression. It affects so many people," he said.

"If ... lots of people know through the media and politics, they see someone like me who says, 'Right, I had this depressive episode, I was able to deal with it and overcome it,' that gives a lot of other people encouragement, both to acknowledge the problems they may have and also to deal with them."

Australian Associated Press