No backroom bureaucrat, he is known for speaking out in support of government policies - and he promotes the idea of the public service as an uncompromising provider of deep-thought policy and advice but one that is conjoined with the government of the day, not ignoring the reality that politics is part of policy.

Malcolm Turnbull's memoir provides insight into his experiences of what it was like to work closely with the senior public servant, who became Home Affairs secretary in December 2017.

Mr Pezzullo first appears in the memoir much earlier when Tony Abbott was prime minister. Mr Abbott and Peter Dutton wanted to give the minister the power to expel an Australian citizen suspected of terrorism. Mr Turnbull believed the plan unconstitutional and morally "unthinkable".

Mr Turnbull says he proposed a change to the Citizenship Act instead, since it already allowed citizenship to be stripped from people who took up arms against Australia for another nation. But the idea was not well received by Mr Dutton and Mr Pezzullo, whom Mr Turnbull describes as "dripping with contempt, almost sneering at me".

He reveals a cabinet discussion on the question in which Barnaby Joyce had said to Mr Dutton, "If we don't have enough evidence to charge someone with terrorism, how can we have enough evidence to cancel their citizenship?" Mr Dutton replied, "That's the whole point, we don't need as much evidence; it's an administrative decision and we don't have to justify it."

Later as prime minister, Mr Turnbull took the decision to combine security agencies under the mega Department of Home Affairs.

At the time, reports suggested the move was pushed by Mr Dutton and long promoted by Mr Pezzullo, but Mr Turnbull describes it as an idea championed by Scott Morrison. George Brandis was reluctant to give more power to Mr Dutton, he says, but the security agencies were more concerned about Mr Pezzullo. They were, in fact, "horrified".

"Pezzullo is one of the most brilliant civil servants in Canberra," Mr Turnbull writes, having a long background working under Labor governments.

"He is a tough-minded intellectual with hardline views on border protection and security issues that could be easily categorised as 'right-wing'."

He "desperately wanted" to succeed Dennis Richardson as Defence secretary and would have been a good choice "except that the uniformed side of Defence were unanimously opposed to him".

"Indeed, I have never known anyone in the Australian Public Service who is more disliked by his senior colleagues than Pezzullo; and yet, in the same breath, his critics acknowledge that he is hard working and gets things done. I found him to give well-considered professional advice."

Mr Pezzullo was "well equipped to bring the new super department together and believed in the concept", but his interpersonal skills were a big obstacle to bringing the agencies together.

Time will tell whether he was the right choice, Mr Turnbull writes.

"I had counselled Mike, as have others, about improving his interpersonal skills and treating people with respect. Almost all of the subsequent grief associated with the creation of the new department has been caused by his, and to some extent Dutton's, authoritarian management style."

As for Mr Dutton, who was made minister, "views may differ as to whether I overestimated his competence, but certainly I misjudged his character."

The Home Affairs Department did not respond to a request for comment.