Staunch republican Peter FitzSimons defends Australia's new Governor-General after she faced criticism for her 43 per cent pay rise

Peter FitzSimons, an outspoken supporter of a republic, has become a surprising ally of the new Governor-General as critics attack the greatly inflated salary she will receive.

Sam Mostyn was sworn in as Governor-General on Monday and will receive a salary of $709,017 for each year of her five-year term - significantly more than the $495,000 paycheck of the outgoing head of state David Hurley.

Ms Mostyn, a climate change and gender equity advocate, reportedly has a close personal friendship with Prime Minister Anthony Albanese.

She will receive a higher salary in the role because, unlike Mr Hurley, she does not receive a large military pension from the Commonwealth on top of the Governor-General salary. 

Mr FitzSimons, the outspoken former head of the Australian Republic Movement, would have been expected to decry such a large salary for the British monarch's official representative in Australia but instead is taking her side in the debate.

Mr FitzSimons defended her salary, noting it was not something she asked for, and also explained it was not, technically speaking, a pay rise.

'Despite all the bloviating and hate, she neither applied for, or received a pay increase on the whim of the prime minister or anyone else,' Mr FitzSimons tweeted.

'The formula says G-G [gets the] same wage as Chief Justice. But previous G-G couldn't double-dip, so military pension [was] deducted from salary.'

While Mr FitzSimons praised Ms Mostyn as a 'woman of the people' despite her vaunted position and significant personal wealth, he had previously criticised the  appointment process, which goes through Buckingham Palace.

'Am I alone in cringing that in 2024 we have to go through this embarrassing palaver?' he wrote on social media in April.

'Asking an English aristocrat if he's okay with our constitutional arrangements is colonial, cringe nonsense.'

Laws setting the salary of the Governor-General passed the House of Representatives last Tuesday with bipartisan support.

However, the Greens spoke out against the size of the pay packet, saying it was out of touch during a cost-of-living crisis.

Greens MP Elizabeth Watson-Brown said workers in other professions would not get a pay rise of 43 per cent.

'Until all women get a 43 per cent pay rise, the incoming Governor-General should not,' she told parliament on Tuesday.

'Who else is getting a 43 per cent pay rise at the moment? It's an absolute insult to people struggling with the cost of living.'

The salary of the governor-general is outlined in the constitution, and is determined by the estimated average salary of the chief justice of the High Court.

The pay level of the head of state is also not increased for factors such as inflation during the length of the term.

Assistant Public Service Minister Patrick Gorman said the governor-general's salary should not be contentious, given long-standing conventions about how it is set.

'I'm sure people would have been surprised if any other proposal was brought forward,' he told parliament.

'Sam Mostyn is an inspired choice, it's been broadly welcomed by the Australian community.'

All four Greens MPs, along with fellow crossbenchers Andrew Wilkie, Bob Katter and Rebekha Sharkie, voted against the salary rise.

Debate on the laws will now shift to the Senate, with the bill set to pass before Ms Mostyn takes on the role.