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He's a petrol-head turned climate change activist but Gareth Hughes, soon to be Parliament's newest and youngest MP, can still appreciate a good car.

The Green Party's Mr Hughes, 28, will be sworn into Parliament in a fortnight to replace departing former co-leader Jeanette Fitzsimons.

He became a convert to the Green way after leaving his hometown of Gisborne to attend Victoria University 10 years ago.

"I was a bit of a bogan before that, a boy racer. I can change an engine on a car."

Since those days he has become a vegetarian, married Meghan and had a son, Arlo, now 2. He no longer has a car - he lives in inner-city Wellington so doesn't need one.

But he concedes there is humour in that history, given he will become the Greens' transport spokesman and will be encouraging cycling and walking rather than increasing the noise a car can make.

But he hasn't quite turned his back on his boy-racer roots.

"I still love cars, I think they're cool. And I'm sure there's a big boy racer vote out there."

He enters Parliament after getting a fairly high list placing of 11 for the Greens in the 2008 election.

He will take over Labourite Jacinda Ardern's title of youngest MP - the 28-year-old Hughes is younger by six months.

His grassroots work began as a volunteer street fundraiser for Greenpeace. It was followed by some short-term contracts and a stint as an adviser to Ms Fitzsimons.

His most recent job was co-ordinating Greenpeace's high-profile Sign On campaign on climate change, ensuring the campaign got publicity, pushing for petition signatures and getting celebrities such as Lucy Lawless and Keisha Castle-Hughes to take on the Prime Minister.

He reckons it has given him valuable experience for Parliament and will help Russel Norman and Kennedy Graham with the climate change aspect of Green Party work.

"It was a really successful campaign. We got to the Government and it was a targeted, simple campaign that delivers."

He has been arrested twice but escaped conviction - first when dressed as Ronald McDonald protesting against GE food and for painting a shipment of palm kernel expeller.