Trade Minister Tim Groser is optimistic the Trans-Pacific Partnership (TPP) deal will be reached by mid-year.
The deal is a step closer after a committee of the US House of Representatives agreed to pass fast-track legislation aimed at facilitating American sign-up to the deal.
'Fast-track' gives a president the power to make trade deals that cannot be amended by Congress. All it can do is accept or reject the agreement.
Supporters have argued that other countries will not negotiate with Washington if they know Congress can amend any deal they agree to.
While the fast-track authority has been described by President Barack Obama and other US trade partners as vital to seal the TPP deal, a full vote on the bill to enable it is not expected until early May.
Mr Groser said there were still difficult negotiations ahead but he was optimistic.
"I assume the professional political managers would have never introduced this legislation unless they were reasonably confident of getting the numbers in the vote," he said.
"I think it's highly likely that we will now enter the end game of this negotiation, which is what New Zealand has been waiting for years, as a result of what's going on in Congress," he said. "I'm reasonably confident that that will result in success."
Mr Groser said he doubted a deal would be struck when ministers from the 12 TPP nations meet in late May but he would bet on a political deal at some point in the middle of this year.
However, Auckland University law professor Jane Kelsey said it was by no means certain that an agreement would be reached in the near future.
Ms Kelsey said the deal still depended on fast-track authority actually being granted to Mr Obama.
She said, in addition, Japan and the US need to reach agreement on a deal for the agriculture and automobile industries for the TPP to move forward.
Ms Kelsey said Mr Groser was in Washington at the moment acting as a kind of wingman for Mr Obama, trying to jolly people along to think there really was a deal in the offing.