Inside, sits a wide-eyed Shane Rattenbury, a kid from Batemans Bay contemplating a world in which he and his mum's rustbucket would struggle to fit.

It was a pivotal moment, one that would set a young Rattenbury on a path to environmental activism and politics, positions of seniority within Greenpeace, and then the leader of the ACT Greens.

His mother, a single parent, uprooted their small family from Batemans Bay to support him, after good grades earned him a low-income scholarship to the prestigious school.

"When I look back now... it was a real gutsy thing to do," Rattenbury said.

"I've said to her, now that I'm older I appreciate the enormity of what she did," he said.

The experience was transformative, shifting aspirations from learning to surf to becoming the first in his family to go to university.

He was accepted to study economics and law at the Australian National University, where an interest in environmentalism and public policy ignited.

He threw himself head-first into environmental activism and scored a job as a lobbyist for Greenpeace, staying to forge a 10-year career, which led to stints in Bangkok and later Europe.

Rattenbury was heading up Greenpeace's oceans campaigns in Amsterdam when he was first approached to run for the Legislative Assembly in 2008.

His first taste of campaigning - working on the Greens' 1995 campaign from a backyard shed - had been successful, and Rattenbury, after some deliberation, agreed and returned to Canberra to win the seat of Molonglo, now Kurrajong.

He was the only Green to survive the heavy losses of 2012, and found himself in the difficult position of kingmaker, helping Labor form government, and taking up a cabinet minister position.

The Green from Grammar would, again, need to find a way to reconcile his past with this new world.

There were, and continue to be, explicit tensions between his role in a Labor-dominated cabinet, and his responsibility to the party and its supporter base.

It is a quandary particularly felt by the Greens, where activist roots breed an inherent distrust of government and pressure for rapid and often-dramatic reform.

But Rattenbury says the arrangement has largely worked.

He goes as far as to say that his activist background and work as a cabinet minister were complementary.

"In some ways, it's the same job, you're there advocating for an issue, putting your case, trying to get others to come on board," he said.

"So for me that move from activism to politics, and then into the cabinet, has not been jarring," he said.

He pauses, and then adds:

"On the whole, I should say."

Yet, in becoming part of the government, he has become tarnished by its decisions, and the Greens have found it a tougher task to shed themselves of Labor's baggage.

In some cases, the arrangement has alienated part of the Greens' traditional voter and membership base. Take his support of the kangaroo cull, for example. It's an issue that he says has split the Greens membership 50:50, angering animal rights-focussed members, but pleasing those who see it as a necessary conservation measure, backed by the science.

"I think for our party, stepping into the executive is a new experience, and has forced us to think about how we approach things," he said.

"Particularly being the only member, I've used the party membership as a touchstone to keep me on track... where issues have come up and there's time, I've actually taken them to general meetings of the party."

"That said, it's not been all plain sailing, and something like the kangaroo cull has really exposed those difficulties."

In other respects, the power-sharing arrangement has given the Greens a tremendous ability to pursue reform. Medicinal cannabis, for example, the 100 per cent renewable energy target, a huge package to clean up Canberra's waterways, the Common Ground affordable housing scheme.

Rattenbury is regarded as a highly capable minister, who has been approached to run federally. Even some within ACT Labor would privately judge him a better ministerial performer than some in their own party.

The Liberals have made much of Rattenbury's ownership of negatively geared investment properties in the Northbourne corridor, promising to refer it to the commissioner for standards if elected, and alleging it may be a breach of the ministerial code of conduct.

"When it becomes very personal, as it has in some parts of this campaign, you don't sign up to politics for that sort of thing," Mr Rattenbury said.

Rattenbury is a long way from his early days of activism, blockading forests in south-east Australia, and bailing others out of jail.

But the flame reignites at times, including when he talks of party elder, close friend and mentor Bob Brown, whose post-retirement work Rattenbury wishes to emulate.

When asked what would have become of him, had he not taken the scholarship at Canberra Grammar, Rattenbury joked that he "would have been a better surfer".

On the tough days, he also think longingly of a peaceful life by the beach.

"There are days, when you think, this is a bit hectic," he said.

"[But] coming up here allowed me to see that broader world view, and I've been involved in a lot of stuff that I really feel has been about putting back, about battling the injustices, creating a better world."

"All of those things, they can sound a bit cliched, but I really feel that's the life I have lived.

"And I've got plenty of it left to do, I've got a good 25-30 years of activism ahead of me, at least."