Former international rugby league player turned environmentalist, Kevin Iro, is a driving force behind the part of the park that will encompass the Cook Islands - a nation whose combined landmass is barely bigger than Washington DC.
"When I was a kid, this was all alive," said Iro, grimacing as he scooped up a lump of dead, grey coral while walking the white sands of a Cook Island beach in the Pacific.
"There were tracks in the coral and if you walked off them you could hear the coral crunching. Now there's no coral here, basically."
The Cooks' Prime Minister Henry Puna formally unveiled the 1.065 million square kilometre (411,000 square mile) reserve when he hosted the Pacific Islands Forum last month, vowing to protect the ocean for future generations.
Puna said the commitment by the tiny nation of 15 islands was its major contribution "to the well-being of not only our peoples, but also of humanity".
Peter Seligmann, co-founder of green group Conservation International (CI), said the establishment of such a large marine park was a courageous move for the Cooks and placed the Pacific at the forefront of ocean conservation.
But to Seligmann the Cook Islands park, while welcome, is just a single piece of the jigsaw.
The American is working with Pacific island states to create a network of similar parks across the region to ensure one of the world's last pristine ocean ecosystems is managed sustainably.
The scale of the proposed network, dubbed the Pacific Oceanscape, is unprecedented - a 40 million square kilometre area stretching from the Marshall Islands in the north almost to New Zealand in the south.
That's about eight per cent of the world's surface area, almost four times larger than Europe and big enough to fit Australia in five times over. It's almost exactly the same size as the surface area of the Moon.
"What we are seeing is the largest conservation initiative in history," Seligmann told AFP. "Piece by piece, nation by nation, it's coming together. It's massive."
Source: US Fish & Wildlife