Mike Kelly's "most prized possession" is his grandfather's loincloth from his time as a prisoner of war on the Burma-Thai railway.

Dr Kelly, who is attempting to reclaim his former seat of Eden-Monaro on July 2, is very much a national security politician, a former soldier who went on to become defence materiel minister and most recently Bill Shorten's defence and security adviser.

But more than any other issue, what's dragging him back is the unfinished business of climate change.

His generation of politicians, he says, need to take responsibility for global warming in the same way that his grandfather's generation took responsibility for fighting the Axis powers.

"That generation made great sacrifices," he said recently over a coffee in an old-school cafe in Queanbeyan, the main population centre of Eden-Monaro.

"I decided this is our big test. We are the first generation to feel the effects of climate change. I felt I could not walk away from that battle … I don't care whether it's popular or not."

Online bookmaker Sportsbet announced on Wednesday Dr Kelly's odds were continuing to shorten, putting him on $1.60 against Liberal incumbent Peter Hendy's $2.25. With punters narrowly backing an overall Malcolm Turnbull victory, the election could break Eden-Monaro's 44-year run as a bellwether, a seat that is consistently won by the party that wins government.

Married with a son, Dr Kelly, 56, says he feels the same kind of responsibility to his son as his forebears felt to his own generation. It's particularly acute for Eden-Monaro, which takes in the NSW ski fields and is one of the most vulnerable parts of Australia to global warming, he said. If Australia lags in climate action, it also risks facing "trade measures" enacted by other countries in the future.

Dr Kelly won the seat in 2007 after ending his military career as a full colonel and head of the army's legal branch. His 20-year career included being awarded the Order of Australia for his service in Somalia, where he famously used his bayonet to fend off supporters of a bloodthirsty warlord who had just been convicted and sentenced to death by a court. He reluctantly quit the army standby reserve recently after being asked by Defence to remove a historical picture of himself in military uniform from his campaign material.

Dr Kelly has some detractors within military circles, something of an inevitability for a military lawyer who has gone into politics. But he is widely liked around Canberra, including among political rivals, with one Coalition candidate telling Fairfax Media: "Mike's a good guy, there are no two ways about it."

He lost Eden-Monaro in 2013 to Mr Hendy, a former senior political adviser and head of the business lobby group the Australian Chamber of Commerce and Industry.

He gave up a job with the United Nations to keep his hand in politics by going to work for Bill Shorten, which involved among other things negotiating waves of new counter-terrorism laws. He came out of that process with "quite a strong respect" for Peta Credlin, the controversial chief of staff to former prime minister Tony Abbott.

"The problem she was having was she was the smartest puppy in the room and a lot of other people around her resented that."

On the national security front, he says "there's still a lot to be done there, frankly", though he won't say what.

He cites US President Barack Obama's sense of urgency about dealing with climate change but treads carefully when asked about Mr Obama's recent remark that global warming is an "existential threat" where the so-called Islamic State is not – an implicit prioritisation that irked US security hawks.

"I would not agree that we have skewed priorities," Dr Kelly said. "Terrorism is an immediate threat that has to be dealt with, with requisite urgency and seriousness. I've seen first-hand this struggle in some of the countries I've worked in. I've lost friends and colleagues to the fight against Islamic extremism.

"But I agree that the climate change threat is the existential threat."

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