ABOUT TIME: John Jolliff, left, and Des Smith, the first Kiwi gay couple to have a civil union, are excited about the marriage equality bill’s third reading.

Sonja Fry and Tania Bermudez Penafiel admit they will be "pretty emotional" tonight as the marriage equality bill looks set to become law.

Labour MP Louisa Wall's Marriage (Definition of Marriage) Amendment Bill is scheduled to have its third reading in the House tonight, and is expected to pass comfortably.

If so, it would make New Zealand the 13th country worldwide, and first in the Asia-Pacific region, to legalise same-sex marriage.

Ms Fry and Ms Bermudez, of Lower Hutt, had a civil union in 2010, but are looking forward to getting married once it becomes legal.

"Tania's already my wife and in our eyes we're already married, but we'll finally be able to put it on paper," Ms Fry said. "A civil union is not quite as good as a marriage but we thought we'd go for it anyway."

While the pair were not planning to have a full ceremony again, it would be a great chance to get their friends and family together to "celebrate equality".

John Jolliff and Des Smith were the first homosexual couple recognised when civil unions were introduced in 2005, but marriage remains their aim.

At present, queer couples were second-class citizens under the law, Mr Jolliff, 83, said.

"No marriages are going to fall apart as a result of our relationship finally being recognised. I just don't understand why it has taken so long."

Mr Smith, 73, said that, if another generation could benefit from marriage equality, it was worth doing.

"There are young people who are struggling, getting booted out of their families, facing bullying. This will be another breakthrough and another slap in the face for those who can't see that a gay relationship is just as valuable as any other."

They would trade in their civil union for a marriage, with a party an essential part of the upgrade, he said.

"I like parties. And this will be another reason for a good party. After all, we're not getting any younger."

St Andrew's on the Terrace senior minister Margaret Mayman, who has performed civil unions since they became legal, was excited at the prospect of extending marriage ceremonies to all.

"On social media and in other circles there's a huge feeling of anticipation, and a feeling that there's a real sea-change about to happen."

She has reserved a spot in the public gallery to watch the vote tonight, but others hoping to score a place will be out of luck - the gallery was booked out well ahead of time. It was also full for both the first and second readings of the bill.

"I've been there for both the other readings," Ms Mayman said. "I think it will be quite a special moment to experience."

The bill passed its committee stage by 77 votes to 43 last month.

If it becomes law, officials will have four months to get paperwork in order, meaning the first same-sex marriage could take place around mid-August.

The Department of Internal Affairs has also confirmed that "bride" and "bridegroom" would remain on marriage forms if the law passed. Additional options were being investigated and would be decided on by the Cabinet if and when new forms were produced.

THE NEW WAY

THE MOVES TO DATE:

1986 Homosexual law reform which decriminalised sexual relations between men.

2001 The Netherlands become the first country to legalise gay marriage.

2004 civil unions law passed here.

2005 First civil unions take place.

WHAT WILL CHANGE?

Gay couples will be able to say they're married. As marrried couples they will be eligible to adopt children, usually children already being raised by those couples.

There will still be brides and grooms.

Celebrants won't be forced to marry same-sex couples if it is against their beliefs.

Churches won't have to hold marriage ceremonies for same-sex couples if they don't agree with gay marriage.

WHICH CHURCHES SAY ...

WE DO

Certain Presbyterian parishes, including St Andrew's on the Terrace, in Wellington

Many Buddhist groups

Quakers

Progressive Judaism

WE DON'T

Catholicism

Anglicanism

Baptists

New Zealand Assemblies of God

Seventh-day Adventists

Jehovah's Witnesses

Church of Jesus Christ of Latter-day Saints (Mormons)

Open Brethren

Sikhism

Islam

Hinduism

Orthodox Judaism