Mr Gaetjens, who finished his role on May 30 after Labor's election victory, also rejected arguments the public service was slow to act on a reform agenda recommended in the recent major Thodey review, and described the reaction to a 2019 speech to public servants by then-prime minister Scott Morrison as overblown.

In a valedictory address at an Institute of Public Administration Australia event in Canberra on Thursday, Mr Gaetjens said it was one of the largest misunderstandings about his roles working in Parliament that they had made him more political.

He said his experience working as a parliamentary liaison officer and, later, chief of staff in ministerial offices, had helped him understand how to deliver policy briefings and advice that were useful to governments.

"What I did was try and connect the public service to the treasurers and ministers that I worked with, to achieve that point where when cabinet, the ministry and the public service, do things in sync, the machine of government hums, and you get good outcomes," he said.

"I regard myself sometimes as a bit of a public service plant up in Parliament House rather than now a political plant in the public service.

"That comment, all of what I said in the speech, is contested. So for those people who know me, those people who want to say something about me, if they think something different, then they can say that and I'm quite happy for them to have that view.

"But certainly from the discussions that I've had with people who know me and how I work, it's that understanding of the process that means you can understand the policy inception to delivery, because unless your policy is delivered as government policy or government statute, it doesn't go anywhere.

"The more that we know as public servants about the whole process rather than just our part of it, I think the better off the whole system."

Mr Gaetjens, who was chief of staff to Peter Costello and Scott Morrison when they were treasurers, faced criticism as Department of the Prime Minister and Cabinet secretary from Labor who said his position leading the public service had been politicised.

Labor's election victory led swiftly to Mr Gaetjens' exit from PM&C, after Anthony Albanese made clear in the campaign he would not keep him as department head and criticised the bureaucrat, saying he made his ongoing position "very difficult" by conducting an inquiry into what the then-prime minister's staff knew of the alleged rape of Brittany Higgins at Parliament House in 2019.

The departure closed a 45-year career in federal and state public services, including roles leading the federal Treasury between 2018 and 2019, and the NSW Treasury from 2011 to 2015.

Mr Gaetjens on Thursday said public servants could not ignore politics, but had to remain neutral.

"We are democracies. People have their political objectives, and you then have to intersect political objectives with policy objectives and outcomes," he said.

Roles working in ministerial and political offices had helped him learn the political process and context of the public service's policy advice, Mr Gaetjens said.

"Whether it's chief of staff or up in political offices, what that gives you is the knowledge of that drumbeat versus the policy drumbeat that we have in departments," he said.

"Once you understand the political process, it helps you do that part of the process in which you're involved.

"If you know what happens to [a brief], then you can actually probably shape the brief so that it gets more attention up in the office, and is aimed to be better absorbed by the minister or prime minister or whoever you brief.

"And if you don't understand that context in which they are working, and just focus on your aspect of the job, well, I think that's falling short of doing the best the public service can do.

"This is not to make the brief political, but it's to make it digestible, consistent with the context in which it's being offered and making the objectives very, very clear."

Mr Gaetjens said the public service had been subject to unfair criticism about the pace of its reform agenda following a major review led by businessman David Thodey.

The secretaries board, which included Mr Gaetjens, advised the Morrison government on its response to the report delivered in 2019. The Coalition government rejected recommendations for major reform including reducing the disparity in pay and conditions for staff working at the same levels across the public service, protecting secretaries from dismissal for political reasons, and requiring more public service experience in ministerial offices.

Mr Gaetjens said the board had crafted an "iterative" reform agenda that also responded to the COVID pandemic.

He read an excerpt of an email from Mr Thodey saying he was encouraged by the public service's progress pursuing the reforms "below the radar", including creating an APS Academy and overhauling the bureaucracy's approach to digital.

Labor has appointed a former Thodey review panel member, Professor Glyn Davis, as Mr Gaetjens' successor in PM&C and appointed former Environment Department secretary Gordon de Brouwer as secretary for public service reform. It said the Coalition government had mothballed the Thodey reform agenda in the previous term of Parliament.

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Mr Gaetjens said he had worked to drive reforms creating more coordination across the public service as PM&C boss, and that the chief operating officers committee had helped bring changes across the bureaucracy. The COVID pandemic and the Black Summer bushfires had also increased the purpose of the secretary's board, he said.

He later told The Canberra Times the secretaries board was maturing into a governance mechanism of the whole public service, rather than a stewardship mechanism.

"But we must look at ourselves to get the strengths out of the 150,000 people that are in the service rather than consider ourselves as working in a 1000 person organisation or a 20,000 person organisation," Mr Gaetjens said.

"We all must understand that there are interactions between the portfolios, we've got to break the silos where we can to actually get that interaction happening to the maximum possible."

Mr Gaetjens in his speech also defended Mr Morrison's 2019 machinery of government overhaul to the public service, reducing 18 departments to 14, saying it provided a more coherent architecture, and that the new government had retained some of its main components.

He described national cabinet as a critical governance mechanism for Mr Morrison and state and territory leaders to share information, make decisions and coordinate actions in the pandemic.

"It may not have been perfect, but I firmly believe it brought more harmony and coherence to the COVID response than otherwise achievable. That national cabinet continues is a positive," he said.

"From an official's perspective, national cabinet meant frequent interaction not only between political leaders, but also between me and my state and territory counterparts."

Mr Gaetjens said he had been deeply saddened by the experiences suffered by staff as revealed in the recent Jenkins and Foster reviews of workplace behaviour in Parliament.

"It will be a mammoth change for parliamentary leaders to shift their focus from the rules and procedures of parliamentary practices to improve staff management and welfare issues," he said.

"But it must be done for the well being and safety of those who work there."

Asked about Mr Morrison's 2019 speech to public servants, widely interpreted as telling public servants their role was to implement and not advise on policy, Mr Gaetjens told The Canberra Times he believed the reaction to the address had been overblown.

Mr Gaetjens said he had not seen the policy advisory role of public servants devalued by successive governments.

"I always think governments will appreciate and expect policy advice from the public service," he said.

Mr Morrison in 2019 told public servants their main role was to implement and advise on policy, and deliver services, not set policy. It was widely seen as a sign of the Morrison government's sidelining of public servants in policy advice. Mr Gaetjens said the speech had a different purpose.

"What the prime minister was then trying to do was to not just say it's policy advice, but it's then once the government has made decisions, it has to be implemented," Mr Gaetjens said.

The federal government's role had involved more than providing funding during the pandemic, and there was a need for greater focus on implementation, Mr Gaetjens said.

"So I thought it was a relative comment, not an absolute comment," he said.