New governor-general Peter Cosgrove may be Australia's best-known military man, but he's long veered clear of politically charged bullets, and is not about to change.

Though reportedly a constitutional monarchist, having referred to the ''silent wisdom'' of Australians after they rejected a republic in the 1999 referendum, he kept his head down on Tuesday, declaring only that his guiding light on such matters would be ''the will of the people''.

And he offered reassurance he'd be staying out of the political fray. ''You are no longer a private citizen in the office of governor-general,'' he said. ''I think your responsibility is to shine light but not generate heat … you're not a participant in the political process.''

General Cosgrove won the Military Cross as a young platoon commander in Vietnam, but remained all but an unknown soldier to most Australians until, 30 years later, he was sent to East Timor.

There, he gained the loyalty of troops under his command, sharing their hardship by occupying a modest camp stretcher; the thanks of the East Timorese - former guerilla leader Xanana Gusmao presented his resistance uniform as thanks, literally giving the shirt off his back - and won the status of hero across Australia.

As the media-savvy commander of the 1999 United Nations-backed East Timor peacekeeping mission, Interfet, then Major-General Cosgrove's military career was suddenly super-charged. He returned to Australia to be appointed Chief of the Army. In 2001, he was

named Australian of the Year.

In 2002, his 37-year military career peaked: he was a full general and Chief of the Defence Force.

A favourite of prime minister John Howard, Cosgrove was considered a contender for the governor-general's position in 2003 when former Anglican archbishop Peter Hollingworth resigned from the job amid controversy after just two years.

Mr Howard chose a former military officer with a Military Cross from Vietnam, but it wasn't Cosgrove. Major-General Michael Jeffery became the first Australian career soldier to be given the job, and maintained a suitably low profile as governor-general.

Meanwhile, General Cosgrove left the military to take up board positions with Qantas and other public companies, wrote a best-selling autobiography, took to the lucrative speaking circuit and was installed as Chancellor of the Australian Catholic University in 2010.

In 2006, he regained national prominence when he took charge of rebuilding north Queensland areas destroyed by cyclone Larry.

It was left to Mr Howard's political protege, Prime Minister Tony Abbott, to cap Cosgrove's career. The new governor-general won't find it hard to navigate around Yarralumla and Admiralty House - in 1972 he served as aide-de-camp to governor-general Sir Paul Hasluck.

Mr Abbott chose the admired military man partly because he was keen to ensure next year's centenary of Anzac Day and Australia's role in World War I was granted a strong vice-regal presence. Cosgrove has the added benefit for Mr Abbott, a keen monarchist, of promising to avoid the sort of hubbub that greeted the current Governor-General, Quentin Bryce, when she embraced the vision of a future republic.

Yarralumla is far from what were the crowded terraces of Paddington, Sydney, where Cosgrove grew up in the 1950s and early 1960s, the son of a soldier. He flunked his Leaving Certificate at the Christian Brothers Waverley College before repeating in order to gain entry to the Royal Military College, Duntroon, in 1965. And, even there, he has publicly conceded, he was ''unfit, untidy, lazy and unpunctual''.

Time and fortune have changed all that. Cosgrove declares the love of his life, wife Lynne, changed everything the first day they met. ''A rough diamond got a bit polished on that day,'' he confided during an ABC interview some years ago.

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