Speaker David Carter has allowed more people into Parliament than is usual for the final debate, with the legislative chambers opened to 200 more people to witness the vote on a live screen.
The New Zealand Herald reports that among those expected to watch the vote are former MPs such as New Zealand’s first transsexual MP Georgina Beyer, the Spanish and French ambassadors and a representative of the US Embassy.
More spectators are expected to gather on the parliamentary lawns.
A majority vote in favour of the measure would make the New Zealand the 13th country in the world to legalise gay marriage.
In February, a New Zealand Parliamentary Select Committee gave the thumbs up to same-sex marriage being legalised in the country. The committee said the bill should progress but with an amendment that ensures no minister was obliged to marry someone against their own beliefs.
The committee received 21,533 submissions on the bill, 10,487 in favour and 8148 against.
The youth wings of New Zealand’s eight major political parties also supported the bill.
Tonight’s vote is expected to take place at approximately 7.30PM (AEST).