[8] Opposition leader David Shearer also declared his support for Wall's bill and said that Labour Party MPs would be allowed to cast conscience votes.

The Committee of the Whole House, where members of parliament debate and vote on the bill clause-by-clause and propose amendments, took place on 27 March 2013.

[20][21] On the day of the vote, conservative Labour MP William Sio moved SOP 202, which sought to uphold the right of individual celebrants to refuse to preside over same-sex weddings, while National MP Tim Macindoe sought to introduce SOP 203, which would widen the 'right to discriminate' on the basis of service provision to conservative Christian caterers, bakers, wedding photographers, public registrars and others engaged in secular occupations who objected to same-sex marriage.

Initial requests to open the Grand Hall immediately outside the debating chamber to cater for the overflow were declined by the Speaker, leaving potentially over 1000 supporters and opponents to overflow onto the Parliament grounds in forecast rain,[27] but later it was decided to open the Legislative Council Chamber with a video link to cater for an extra 200 people.

[26] Despite being one of six openly gay MPs himself, Attorney-General Chris Finlayson voted against the bill, declaring his opposition to state involvement in the institution of marriage as the reason.

[29] After presiding Speaker Lindsay Tisch read out the result of the vote, the public gallery broke into singing "Pokarekare Ana", a Māori love song (waiata), later being joined by some MPs on the floor.

[32] During the third reading debate, Building and Construction Minister Maurice Williamson (National, Pakuranga) took a five-minute call and gave a jovial speech, pointing out logical fallacies in some of the more aggressive statements by opponents – the last of which he disproved that the bill was cause of the recent drought conditions affecting New Zealand, by pointing out that it was raining in his electorate that morning, complete with a "big gay rainbow".

The speech became a YouTube hit, and was viewed hundreds of thousands of times over the next few days, featuring on high-profile news sites like The Huffington Post and Gawker.

The New York Times also picked up the story, incorrectly stating that Williamson was "one of New Zealand's only openly gay MPs" (he is actually heterosexual, and married with three adopted children).

Williamson said he also received an expenses-paid offer to go on The Ellen DeGeneres Show, but he turned it down due to scheduling conflicts.