New Zealanders will vote on whether euthanasia should be legalised next year after a long-fought bill passed 69 to 51.

If endorsed by the public in a referendum the new law will allow those who are terminally ill to request assisted dying.

The patient must be the first to suggest assisted dying, and two doctors must agree that the patient is well-informed and other legal criteria are met.

The End of Life Choice Bill, sponsored by lone ACT MP David Seymour, passed 69-51 on Wednesday evening.

As Labour and National treat euthanasia as a "conscience issue" their MPs voted freely on the bill. Labour MPs were much more likely to support the bill: 33 Labour MPs and 17 National MPs voted in support, as opposed to 38 National MPs and 13 Labour MPs against.

The Greens and NZ First both agreed to vote for the bill on-bloc once certain conditions were met.

We lost a battle and now it has escalated. We will not give up.

For the Greens those conditions were more safeguards to make sure only the terminally ill were covered, and could not be coerced.

NZ First meanwhile demanded a referendum on the subject, an amendment entered by a tight vote won 63 to 57.

ANTI-SIDE PROMISE WAR

National MP Maggie Barry, one of the bill's fiercest opponents, said her side had lost a battle but the war for the referendum had just begun.

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"The most liberal Parliament in New Zealand's history has voted through this dangerous and permissive bill. Now the only hope of stopping euthanasia being legalised is through a referendum at the election," Barry said.

"We are involved in now, a major war to tell the people of New Zealand what this might mean for the vulnerable, for the disabled, for those who fear for their lives.

"We lost a battle and now it has escalated. We will not give up."

Seymour also said it was the start of a referendum campaign.

"It's also the point where it became possible for the New Zealand public to choose choice, and become more of a civilised society," Seymour said.

"My message to people who are genuinely concerned about this is they have absolutely nothing to fear. This bill has robust safeguards.

"It is entirely about choice. Just as their rights and choices are respected, they will also need to respect the choices of others."

Asked if he had a final message for Barry, Seymour suggested she return to her garden.

LECRETIA'S MOTHER: SHE WOULD HAVE BEEN PROUD

Lecretia Seales was a terminally ill lawyer who inspired the bill after suing the Government for her right to die in 2015.

Her mother Shirley was in the House to watch the debate and told Stuff afterwards she would have been proud.

"I know that Lecretia started conversations and things wouldn't have happened but I didn't think they would happen - you might not call this quickly - but it could have taken a lot longer.

"It was just magic to have it happen with that margin.

My message to people who are genuinely concerned about this is they have absolutely nothing to fear. This bill has robust safeguards.

"[Lecretia] would so be proud. She was someone who was really well-reasoned. Who based things on absolute fact. She would have been so so happy today."

Lecretia's lawyer from the original case, Catherine Marks, said she never thought the case would end up as a bill.

"To me this is Lecretia's legacy. Her case provided the evidence that allowed this bill to go this far."

EMOTIONAL DEBATE

MPs from both sides of the debate made emotional speeches in favour and against the bill ahead of the final vote on Wednesday night.

National MP Chris Bishop, a key backroom figure in helping the bill pass, said the status quo was "fundamentally intolerable".

"I do not accept the argument that has been put by some - that painful death is just something we should blindly accept, that it is 'God's Will'. Pain is a part of life; but it seems cruel and heartless to try and not ameliorate suffering when we can do so," Bishop said.

He cited research which suggested that between 3 and 8 per cent of suicides in the 20th century were committed by people who were "rational, competent, and suffering a terminal illness".

Fellow National MP Shane Reti, a fierce opponent and a GP, said he didn't want to have the "spectre of euthanasia looming over every single consultation."

He recalled huge human endeavours made by people who had less than six months to live - and would thus have been eligible for euthanasia.

"In 1827, Ludwig Beethoven was dying with cirrhosis of the liver. He was eligible for euthanasia, and yet in his final months he completed some of his most admired work, including the substitute final movement of the String Quartet No. 13. Under euthanasia, this brightness would be gone from the world."

Reti and Labour MP Adrian Rurawhe said the bill would hurt Māori as they had disproportionately bad health outcomes.

"It will disadvantage Māori further in a system which already disadvantages Māori. The health inequities are significant. We cannot continue to pass bills that continue to affect Māori and others in that way," Rurawhe said.

This was rejected by Labour MP Willie Jackson, a swing vote who supported the bill, who said there was no one single tikanga.

FOUR-YEAR JOURNEY TO PASS BILL

The bill was put in the members ballot in 2015 following Seales' court case.

Seymour's bill has had a massively contentious ride through Parliament since being pulled from the ballot in 2017.

It went through a 16-month select committee - the longest ever - with a record 39,000 submissions, yet emerged almost unchanged after massive disagreements between the MPs considering it.

Instead several amendments Seymour was keen to make on his own bill - generally narrowing its scope to keep other MPs on board - had to be made in Parliament itself, and a group of supportive MPs trusted to support his changes.

The most momentous of these was a change to make the actual decision dependent on a referendum, which is essential for keeping NZ First and its nine votes in support.

That change - reviled by many who supported the bill - passed narrowly, 63 votes to 57, just two over the 61 vote majority required.

National MP Nick Smith, one of the main opponents of the bill, attacked the presence of a referendum.

"The liberals who want this to pass do not have the numbers without a referendum," Smith said.

"The liberals who want abortion to pass do not need those numbers."

Three MPs switched their votes between second and third reading. Kiri Allan of Labour went from no to yes while National's Lawrence Yule and Labour's Poto Williams went from yes to no.

BY THE NUMBERS

AYES (69):

Labour (33): ARDERN Jacinda, DAVIS Kelvin, LITTLE Andrew, ROBERTSON Grant, WOODS Megan, HIPKINS Chris, SEPULONI Carmel Jean, PARKER David, NASH Stuart, RADHAKRISHNAN Priyanca, HUO Raymond, LEES-GALLOWAY Iain Francis, TINETTI Jan, PRIME Willow-Jean, FAAFOI Kris, JACKSON Willie, CURRAN Clare, DYSON Ruth, WALL Louisa, ANDERSEN Ginny, LUXTON Jo, CRAIG Liz, LUBECK Marja, MALLARD Trevor, EAGLE Paul, COFFEY Tamati, McANULTY Kieran, WARREN-CLARK Angie, O'CONNOR Greg, MAHUTA Nanaia, HENARE Peeni, WEBB, Duncan, ALLAN Kiri.

National (17): ADAMS Amy, BENNETT Paula, BISHOP Chris, COLLINS Judith, DOOCEY Matt, FALLOON Andrew, HUDSON Brett, KAYE Nikki, KING Matt, KURIGER Barbara, MITCHELL Mark, SIMPSON Scott, SMITH Stuart, STANFORD Erica, VAN de MOLEN Tim, WILLIS Nicola, YANG Jian.

GREEN (8): SHAW James, DAVIDSON Marama, GENTER Julie Anne, SAGE Eugenie, HUGHES Gareth, LOGIE Jan, SWARBRICK Chlöe, GHAHRAMAN Golriz.NZ FIRST (9): PETERS Winston, MARK Ron, MARTIN Tracey, TABUTEAU Fletcher, BALL Darroch, MITCHELL Clayton, PATTERSON Mark, JONES Shane, MARCROFT Jenny.

ACT (1): SEYMOUR David

INDEPENDENT (1) : ROSS Jami-Lee

NOES (51):

National (38): BAKSHI Kanwaljit Singh, BARRY Maggie, BAYLY Andrew, BENNETT David, BIDOIS Dan, BRIDGES Simon, BROWN Simeon, BROWNLEE Gerry, CARTER David, DEAN Jacqui, DOWIE Sarah, GARCIA Paulo, GOLDSMITH Paul, GUY Nathan, HAYES Jo, HIPANGO Harete, LEE Denise, LEE Melissa, LOHENI Agnes, MACINDOE Tim, McCLAY Todd, McKELVIE Ian, MULLER Todd, NGARO Alfred,O'CONNOR Simon, PARMAR Parmjeet, PENK Chris, PUGH Maureen, RETI Shane, SCOTT Alastair, SMITH Nick, TOLLEY Anne, UPSTON Louise, WAGNER Nicky, WALKER Hamish, WOODHOUSE Michael, YOUNG Jonathan, YULE Lawrence.

Labour (13): ALLAN Kiri, CLARK David, KANONGATA'A-SUISUIKI Anahila, O'CONNOR Damien, RURAWHE Adrian, RUSSELL Deborah, SALESA Jenny, SIO Aupito Tofe Sua William, STRANGE Jamie, TIRIKATENE Rino, TWYFORD Phil, WHATIRI Meka, WOOD Michael Philip, WILLIAMS Poto.