Former Commonwealth Secretary-General Don McKinnon believes a merger with Australia is inevitable.
A recent poll has found 40 per cent of New Zealanders support a debate about becoming a state of Australia.
The UMR Research poll surveyed a thousand people on both sides of the Tasman.
Approximately a quarter of Kiwis favoured the country becoming part of the Australia with 71% opposed to the idea.
37% of Australian respondents supported the merger, compared 52% against it.
Sir Don - who is also a former Foreign Affairs Minister and chair of the Trans-Tasman Business Circle - told TVNZ's Q&A programme that it was just a matter of time before a formal agreement is reached with Australia.
"We've got nearly half a million New Zealanders living in Australia anyway," he said.
"By the time the next generation comes around, technology and the movement of people everywhere, New Zealanders won't want to be in the situation of paying taxes in both countries and all the time going through immigration and Customs. They'll want to try to eliminate all those things."
Sir Don believes the shift will be people-driven, rather then politically motivated.
"It's a debate that's going to go on, but no political leader in New Zealand is going to win an election advocating this issue."
But Labour party leader Phil Goff said there was no reason for a union with Australia.
He said although Australia had nothing to lose from it, joining with a much larger country would mean giving up our national identity.
"New Zealanders are proud of their culture, they are proud of their history, they are proud of their sense of identity."
He said working towards a single economic market between the countries could be achieved without a merger.
"When we can get the benefits of a closer economic relationship and a single economic market, what are the additional benefits of simply being the seventh state?
"It's about making decisions in New Zealand for New Zealanders by New Zealanders that really matter. We can have a closer relationship, we can get the best of both worlds. Submerging ourselves into Australia is not required to achieve that."
Former Prime Minister Mike Moore said New Zealand simply had to "toughen up".
"We will not solve our economic problems by becoming a state or two states of Australia."
- NEWSTALK ZB, NZHERALD STAFF