Parliament has passed a fiercely debated bill legalising assisted dying, with the public to now make the final decision on the legislation next year.

The End of Life Choice Bill passed 69 votes to 51 at its third and final vote in the House on Wednesday night and will now to go to referendum alongside the 2020 general election.

So how would assisted dying work and what happens now?

What is the End of Life Choice Bill?

It's a piece of legislation introduced by Act leader David Seymour that would make it legal for people to request assisted dying, or euthanasia, from doctors, and legal for health practitioners to help people die under certain conditions.

Who would be able to ask for assisted dying?

The option would be open to those who have been diagnosed as terminally ill and with less than six months left to live. It originally also covered people with "grievous and irremediable" conditions, but got narrowed down to get more support in Parliament.

How would assisted dying actually work?

Doctors and nurses are banned from starting conversations about euthanasia under the law, so a patient has to request it themselves.

They would have to go through a series of checks with two doctors, including one appointed through the Ministry of Health.

If the patient meets all the criteria, they get given a form to return, if and when they've picked a time, place and method for how they want to die. They have six months to use it and if they don't, they have to go through the whole process from the start.

Patients can choose whether to have the drugs delivered intravenously, by mouth or tube and whether to trigger it themselves or have a doctor or nurse do it at a place of the patient's choosing, including at home.

Health practitioners are allowed to opt out of participating in any part of the process and the bill states they're not meant to penalised by their employers for doing so.

Can you change your mind?

Yes. Patients are allowed to change their minds at any point.

What's been the major concerns?

Opponents of the legislation have raised several issues but the most common has been about coercion.

They say the bill lacks the proper safeguards to protect vulnerable people from pressure to take up assisted dying. They argue it would put subtle pressures on the ill or elderly, particularly if they are made to feel like a burden, and open them up dangers from more overt forms of coercion.

The bill includes clauses saying doctors have to stop the process if they suspect coercion, but critics argue physicians may not know patients well enough or be properly trained to make the call.

How would it be policed?

All assisted deaths would leave a paper-trail that would be collected by a Ministry of Health-appointed registrar. They would check every death, keep data and report any concerns to medical oversight bodies or even the police.

So what happens now?

A public referendum will now be held alongside next year's general election to decide whether the bill should become law.

The bill has been subjected to heated debate in and outside of Parliament for nearly two years and it's expected campaigning will ramp up even further next year.

Many MPs who supported the legislation only grudgingly backed it going to a referendum because it was the only way to get enough support in Parliament.

Historically, polls have showed there's majority support for some form of assisted dying in New Zealand. But the referendum will ask people whether they specifically support the End of Life Choice Bill and it's not clear what effect that might have.

Justice Minister Andrew Little has said the Government will try to provide objective information to the public ahead of the vote.