Questions have been raised about Ms Campbell's appointment to the senior Defence position following the role she played in the robodebt saga under the former Coalition government.

Department of Defence secretary Greg Moriarty revealed in Senate estimates on Wednesday afternoon he was warned by Department of Prime Minister and Cabinet secretary Professor Glyn Davis that Ms Campbell's removal as DFAT secretary was "likely".

Mr Moriarty said he told Professor Davis he believed there "was a role for her in the defence portfolio in the nuclear-powered submarines task force".

The top Defence official defended his decision, saying it was an "appropriate role" for Ms Campbell who he described as "a very experienced and senior public servant".

"In [the] very early days of his tenure as the secretary of Prime Minister and Cabinet, I raised with secretary Glyn Davis, the fact that I was anticipating some large challenges with the submarine task force," Mr Moriarty said.

"He subsequently contacted me on the 14th of June to establish whether there might be a role for Ms Campbell given that she was likely to be moving, or transferred from her position as the secretary of the Department of Foreign Affairs and Trade.

"He asked me to think about whether there was an appropriate role."

READ MORE:

Tasmanian senator Jacqui Lambie pressed the department's top officials over the decision, questioning Ms Campbell's suitability in reference to evidence she gave at Royal Commission hearings into the illegal robodebt scheme.

The Royal Commission is expected to present its findings into the income-averaging scheme that affected hundreds of thousands of Australians to Governor-General David Hurley on July 7.

Senator Lambie described Ms Campbell's role on the nuclear-powered submarine taskforce, which she commenced in June 2022, as a "slap in the face" to those affected by the scheme.

"Oh, my God, what were you thinking?" Senator Lambie said.

"Some of you people [have] been in this job for too long, because I think you're starting to lose your wits."

Internal emails and documents obtained under a freedom of information request by former South Australian senator Rex Patrick revealed earlier this month the AUKUS advisory role and associated paperwork was signed off just days after Prime Minister Anthony Albanese announced Ms Campbell's time running the Foreign Affairs Department had come to an end.

In a letter addressed to then-public service commissioner Peter Woolcott, Mr Moriarty wrote Ms Campbell fulfilled the requirements of "a highly experienced leader with very specific credentials".

The Defence secretary proposed Ms Campbell's existing full salary package - which amounted to around $900,000 - be brought over for the "critical nature of the position and experience Ms Campbell will bring".

A review into whether the role will be expanded beyond its three-year term is expected to take place in 2025, the letter said.

Mr Woolcott approved the request two days later.

We've made it a whole lot easier for you to have your say. Our new comment platform requires only one log-in to access articles and to join the discussion on The Canberra Times website. Find out how to register so you can enjoy civil, friendly and engaging discussions. See our moderation policy here.