"I know from direct experience that living without electricity is incredibly difficult," PNG Prime Minister Peter O'Neill said at the signing ceremony on Sunday.
The mountainous PNG is notoriously difficult for infrastructure projects, with the vast majority of the population living in remote or rural areas.
The capital Port Moresby is also cut off from the rest of the country, and can only be reached by sea or air.
Australian Prime Minister Scott Morrison said he had sat in remote villages and had some understanding of how hard it was to live without power.
"It's time to power up PNG right across the country," he said.
Papua New Guinea will choose its own power sources, but it currently uses 70 per cent hydro.
NZ Prime Minister Jacinda Ardern said the project would unlock opportunities for women, while US Vice President Mike Pence said quality of life in PNG would improve.
The project will require large-scale public and private investment in new generation, transmission lines and distribution.
The deal is the first to be funded under the tri-lateral infrastructure deal announced last week between the US, Japan and Australia.
But it will also be open to other nations that support "a free, open, prosperous and rules-based region."
The project comes as China increases its infrastructure push into PNG, including hospitals and a major road in Port Moresby.
But locals have criticised China for building unnecessary projects that don't help the community - the road China ripped up and replaced was already one of the best in PNG.
The Chinese projects have also been funded with "aid money", but they are built by Chinese workers, using Chinese materials, and the money goes back to Chinese companies.
Australia will commit $25 million in the first year, and will ensure fibre optic cable is rolled out as part of the grid.