ACT party leader will support a change to his bill on legalising euthanasia in order to get New Zealand First's support for it.
Mr Seymour's End Of Life Choice member's bill could possibly come before Parliament tonight and if not, it will be debated early next year.
Mr Seymour said New Zealand First asked him to change his bill to include the requirement for a public referendum before it became law, in return for its nine votes.
Mr Seymour said he thought a referendum could take some heat out of the issue.
"A lot of members of Parliament are feeling a lot of pressure and if they knew the final tick off would be by the people of New Zealand maybe that would reduce the pressure.
"But I can also tell you that with 75 percent of New Zealanders consistently saying they support choice we would win a referendum."
Mr Seymour said if the amendment was passed the referendum would take place at the next General Election.
"My strong preference, and I'm sure [New Zealand First leader] Winston Peters would agree, is to do it in conjunction with a General Election - we don't want to spend taxpayers' money unnecessarily."