Phil Goff says Helen Clark is our "best chance ever" of having a Kiwi run the United Nations.
Mr Goff says he'd even take time out of his Auckland mayoralty campaign if it'll help her win arguably the world's top elected position.
"If I was asked to do anything on her behalf and on behalf of New Zealand, of course I'd do that," he told Paul Henry this morning.
"I don't think it'll come to that, but I'd be happy to put my voice behind her in anything that she needs."
The ex-Labour Party leader hasn't been approached by the Government yet.
Prime Minister John Key, who defeated both Ms Clark and Mr Goff in general elections, has given Ms Clark the Government's full support -- something Mr Goff hasn't always done when it came to internal Labour Party politics.
In 1996, he was part of a group that confronted Ms Clark over her dismal poll ratings since taking over from former leader Mike Moore.
"Take the context of the time -- Helen was I think on 1 percent in the polls as leader of the Opposition; Labour was on 14 percent. We went to Helen -- we were all friends of Helen actually, there was people like Michael Cullen, Annette King and myself -- we went in, we said, 'Helen, we don't think you're going to make it. We think you're going to have to step aside.'"
In his opinion, that challenge directly led to her later success.
"That was a catalyst for her to renew her determination and her commitment to go for the job that she really loved," says Mr Goff.
"I think she would acknowledge now that was the turning point for her from doing dismally to picking up her act and going forward. She didn't win in 1996, but she did win spectacularly in 1999… That shows I think the steel core, the determination, the toughness of the woman."
The main obstacle Ms Clark will have to overcome will be politics, rather than proving that she can do the job well, says Mr Goff.