New Zealand's parliament has passed marriage equality legislation, making it the first country in the Asia-Pacific region and the 13th country worldwide to legalise same-sex marriage.

The bill, which passed 77 votes to 44 on Wednesday, redefines marriage as a union between two people, rather than a man and woman.

National Party prime minister John Key backed the legislation, which was introduced by Labour MP Louisa Wall.

Ms Hall says the law change has widespread public support, particularly among young people.

She says it shows just how far public opinion has come in New Zealand.

"Nothing could make me prouder to be a New Zealander than passing this bill," she said.

Same-sex marriage is legal in: New Zealand, 2013

New Zealand, 2013 Uruguay, 2013

Uruguay, 2013 Denmark, 2012

Denmark, 2012 Argentina, 2010

Argentina, 2010 Portugal, 2010

Portugal, 2010 Iceland, 2010

Iceland, 2010 Sweden, 2009

Sweden, 2009 Norway, 2009

Norway, 2009 South Africa, 2006

South Africa, 2006 Spain, 2005

Spain, 2005 Canada, 2005

Canada, 2005 Belgium, 2003

Belgium, 2003 The Netherlands, 2000

In total, leaders of seven of the country's eight political parties supported the change.

It is due to take effect within four months, which means gay couples will be able to legally wed in New Zealand as early as August.

The law change would also open the door for married gay couples to adopt children.

Earlier, Marriage Equality New Zealand spokesman Conrad Reyners said it was a landmark day.

"I think a successful vote tonight will show that members of the queer in New Zealand, their lives have meaning and their lives have value just like any other citizen in New Zealand as well," he said.

Throughout its course in parliament the bill received huge cross-party support.

Gay rights advocates say it is an historic occasion and that they are proud it is happening in New Zealand, but there have been some campaigns against the bill.

A Protect Marriage campaign recently took out a full-page advertisement in national newspapers, saying if the bill was passed into law it would make marriage "meaningless" and would be an act of "cultural vandalism".

New Zealand's Presbyterian Church officially opposes the redefinition of marriage, however it is allowing ministers to make their own call on the issue.

But the church says if ministers do choose to marry people of the same sex, there is a possibility it will be open to challenge.

'Game-changer'

Sorry, this video has expired Same-sex marriage 'inevitable' in Australia

The Australian Marriage Equality lobby group says hundreds of same-sex Australian couples are now planning to head to New Zealand to tie the knot.

The group says it knows of 1,000 couples who have so far expressed an interest in crossing the Tasman to wed.

But spokesman Rodney Croome says once they returned to Australia, their marriages will not be recognised.

"It's wonderful for them that they can marry so close to Australia, but of course all of those couples would prefer to marry in the country they love with their family and friends nearby," Mr Croome said.

Mr Croome says the New Zealand decision will be a "game changer" when it comes to the debate on same-sex marriage in Australia.

"This will increase pressure on our politicians to take action," he said.

"Australians will be saying 'we need to catch up', our politicians need to do the same."

Conscience vote

Mr Key gave MPs a conscience vote on the issue.

When similar legislation was voted on in the Australian Parliament, the Coalition did not allow MPs a conscience vote.

"If the Coalition here in Australia did the same thing, then this reform would have a fighting chance in our federal parliament," Mr Croome said.

He says the Coalition is only blocking the inevitable.

"When it is a country so close to us like New Zealand, when there is so much interaction between the two countries... I have no doubt that we will also move towards that," he said.

"I just wish that at a federal level our politicians could see the advantage to them and to the nation of allowing this.

"If they don't then I'd say it is inevitable that this will occur first at a state level in Australia because Australian policy makers and the people can no longer wait."

While holding a community cabinet meeting in Ringwood in Victoria, Prime Minister Julia Gillard was tonight told that Australia would have liked to "beat" New Zealand on same-sex marriage.

"What we have done is as a political party we've decided that people can exercise their own views and their own conscience when this matter comes before the parliament, which it recently did and I'm sure it will again in future," she said.