Helen Clark says the process for choosing the United Nations secretary-general has the appearance of transparency, without being genuinely open.
Miss Clark failed in her bid to win the job last year.
RNZ's Sunday Morning programme spoke to Miss Clark and filmmaker Gaylene Preston who documented the whole process of her bid in My Year With Helen.
Miss Clark told Sunday Morning she was the best performer in the debates between candidates, and in a vote of UN staff, but none of that had mattered.
"This process had the appearance of transparency when it was anything but and in some senses it almost made it worst because it gave the appearance of being open with candidates, openly presenting and the big Al Jaazera debate and so on, but actually none of that had the slightest bit of impact on the decision.
Miss Clark said she did extremely well in the presentation and debate and was probably one of the top two performers (the other being Antonio Guterres).
"None of that mattered because the decision was made in the security council and particularly in discussion between the five permanent members and they give one name to the general assembly that votes it up or down - it's never going to vote it down, it takes the one name, with the 10 elected members playing the bit role."
Instead Miss Clark said Antonio Guterres was selected through secret discussions between the permanent Security Council members, the United States, the United Kingdom, Russia, France and China.
"In my opinion the radical change would be to have the UN General Assembly empowered to make the decision, you have continuous balloting on preferential basis until someone emerges with a majority."
She said that was probably not very likely which was sad because if the UN didn't move with the times then it would become irrelevant.
Filmmaker Gaylene Preston documented the whole process and her film My Year With Helen became a study of gender politics and an insight into the closed world of international diplomacy at the United Nations.
The film is in cinemas on 31 August.