Politicians look set to make history this week with gay marriage likely to become legal.
However, the first wedding will not take place until mid-August.
Labour MP Louisa Wall's marriage equality member's bill is due to have its third reading in Parliament on Wednesday night.
The bill passed its committee stages with 77 votes to 43 last month and little change was anticipated for the final vote.
Big crowds, including a few celebrities, were expected to be in Parliament's public gallery to witness the vote.
Kapiti Mayor Jenny Rowan and her partner, Jools Joslin, will be there. They went to the court for the right to marry, but lost.
Green MP Kevin Hague said there had been a groundswell of support not only from same-sex communities but from straight people as well.
"I just feel enormously grateful to them because they have no personal stake in it, they just say this is the right thing to do."
The passing of the legislation was historic and would remove the last remaining legal inequalities for homosexual people, Hague said.
"After this bill passes we will effectively have equality under the law, which is one of the basic human rights."
Viewing parties and celebrations were planned to be held around the country if the bill does pass, Hague said.
The Conservative Party and lobby group Family First are both running publicity campaigns against same-sex marriage.
Family First spokesman Bob McCoskrie wants people to sign a "marriage pledge" saying they will not vote for an MP or political party that supports Wall's bill.
"The definition of marriage should stay as traditionally and commonly conceived - not one manipulated by politics and political correctness."
Gay marriage is a conscience issue, meaning MPs can make up their own minds how to vote rather than following a party line.
If passed, officials would have four months to get the paperwork in order before the first same-sex couple could marry.