David Seymour says three quarters of Kiwis would support voluntary euthanasia in referendum

ACT Party leader David Seymour says he believes three in four Kiwis would support his voluntary euthanasia legislation and suggests a binding referendum be incorporated into the next General Election.

Mr Seymour's End of Life Choice Bill passed its first reading in parliament last night, with MPs casting 76 conscience votes in favour and 44 against the bill.

The bill gives people with a terminal illness or a "grievous and irremediable" medical condition the right to request assisted dying, and also defines those eligible and details a comprehensive set of provisions to ensure it is a free choice made without coercion.

It also outlines a stringent series of steps to ensure the person is mentally capable of understanding the consequences of their decision.

Mr Seymour, speaking this morning to TVNZ 1's Breakfast today, said support among the New Zealand public for assisted euthanasia "consistently runs at 75 per cent".

"The public will be invited to make submissions on the bill - there's already been an inquiry about the broader topic," he said.

National Party leader Bill English strongly opposes the bill, and Mr Seymour said his parliamentary ally was "wrong" on this occasion, despite them agreeing on most things.

I've discussed it with him - a bit cheekily - when I first thought of putting the bill in and he said 'well, that's why you're in a different party' and I said 'that's probably about right'," Mr Seymour said.

"We've worked very closely together on a range of things, we're allies on most issues, on this particular issue I just think Bill English is wrong and there's a lot of people within the National Party and National Party voters ... who want choice on this too."

Mr Seymour said a referendum on the issue is "a possibility".

"I've got an agreement with New Zealand First to promote the idea of a referendum - it would be binding," he said.

"The way it would work is that the bill would go through parliament and then having been voted on by MPs there would be a question at the end - this bill becomes a law only after a majority of New Zealanders vote on it.

"So at the next General Election there might be an extra box to tick."

He said doing it as part of an election rather than as a standalone referendum would be "almost costless".

"I'm confident that if there was to be a referendum then we would pass."

The bill will now go to a select committee for public submissions.