They would also ensure electoral officials and ballot boxes could be delivered to remote areas.
Mr McCully was not sure whether they would be armed, but said: "The [troops] will be there for peaceful purposes, not deployed in the sense that they're expecting to be dealing with trouble."
Asked whether they would stay longer if PNG became more unstable, he said: "We'll do whatever we have to to make things work."
He said NZ Aid would fund charter boats to transport electoral commission staff and supplies to remote locations.
PNG has suffered great political instability in the past year. The incumbent, Peter O'Neill, was sworn in again as Prime Minister yesterday for the third time after a Supreme Court ruling that former Prime Minister Sir Michael Somare was the legitimate Prime Minister.
There are questions over whether that swearing in was legitimate because Parliament had already been prorogued before its dissolution for the elections.
Mr O'Neill took over last year during Sir Michael's lengthy absence because of illness.
The police last week arrested the Chief Justice and charged him with sedition for a judgment in favour of Sir Michael.
Mr McCully said that over recent months Papua New Guinea had had two Prime Ministers, two Cabinets, two police commissioners, two chiefs of defence force on some days of the week "and that is one too many of each of those".
He said it was important that the people of PNG had confidence in the outcome of the elections.
New Zealand would also provide a small team of election monitors, Mr McCully said.
"Both New Zealand and Australia are pleased to help a Pacific neighbour undertake a successful general election - it is important that we assist in whatever way possible."
Australia has a long history of assistance in Papua New Guinea.
Australian soldiers have aided the country during times of natural disaster, such as the PNG Assist mission in 2007 after severe floods.
The two countries began a policing partnership in 2008, with Australia providing training and support services to improve the capabilities of the PNG police.
Last year Prime Minister Julia Gillard agreed that Australia would provide federal police support during this year's elections, including assistance with planning and the training of police officers.
