Speaking to the General Assembly in the annual round of the nation speeches to the United Nations in New York overnight, Mr McCully said it was difficult to overstate the level of frustration "of the people I represent" with the complete inability of the United Nations Security Council to act in relation to Syria.
He questioned what it took for the Security Council to act when 25,000 deaths, countless thousands injured and many more thousands displaced and homeless did not prompt the Security Council to act.
"In the absence of leadership from the Security Council, I suggest that this [General] Assembly will need to find ways to play a more activist role."
The case for reform of the Security Council had become "utterly compelling", he said.
"Indeed, increasingly, the future credibility of the United Nations may depend upon it."
He called for the P5 - the five permanent members of the Security Council; America, Russia, China, France and United Kingdom - to voluntarily accept restrictions of the use of veto.
"To ask the P5 to acknowledge and respect the genuine concerns of the wider membership by voluntarily accepting a curb on the exercise of the veto, is an entirely reasonable and achievable objective," he said.
Routinely the veto was used in circumstances which had little to do with national interests, but Mr McCully said the Security Council should consider a process which restricted the veto use to issues which clearly and directly affected national interests.
Mr McCully told TVNZ's Q+A that when he delivered his speech and spoke about restricting the use of veto some of those listening broke into sporadic applause.
"It's clear that the amount of people who came to raise matters with me subsequently that it's something that tapped into a bit of a nerve here, I think there's a real sense of frustration."
However, he was not particularly optimistic that the Security Council would budge about Syria.
Both China and Russia have used their vetoing powers in relation to Syria.
His speech comes as New Zealand campaigns to get a seat on the Security Council in 2015/16, and Mr McCully said New Zealand had paid its dues.
"We've got a campaign that's been underway for quite a long time...our level of support's good, but of course we'll come under a lot of pressure coming into the next two years."
New Zealand had some great "friends" internationally, he said.
"I simply say that we're right in this contest...It's not going to happen without a lot of hard work."
He would not be drawn on how confident he was that New Zealand would get a seat.
