The will of the Scottish Parliament “must and will prevail” over a new independence referendum, Nicola Sturgeon is to tell the SNP conference.
MSPs will debate calling for permission for a vote on Tuesday and Wednesday, with the motion expected to pass.
Theresa May has said “now is not the time” for a second referendum.
The first minister will tell delegates in Aberdeen that refusing this call would “shatter” any notion of the UK as a partnership of equals.
A second referendum has become the focus of the conference after the UK government said it would reject Ms Sturgeon’s call for a vote between Autumn 2018 and Spring 2019.
Mrs May argues that it would not be fair to hold a referendum before the state of the UK outside of the EU becomes clear so voters can make an informed choice.
But the SNP leader will tell delegates that “Scotland’s future must be Scotland’s choice”, citing an SNP manifesto pledge that there could be a new referendum if there was a “significant and material” change in circumstances.
She is expected to say: “Next week, in line with the mandate secured at last May’s election, we will ask the Scottish Parliament to agree that the Scottish people should have the right to choose our own future.
“We will ask parliament to agree that this choice should be exercised at a time when we know the terms of Brexit but before it is too late to take a different path. And we will ask parliament’s permission to seek the legal authority that will allow the people of Scotland to have that choice.
“If a majority in the Scottish Parliament endorses that position, the prime minister should be clear about this. At that point a fair, legal, agreed referendum – on a timescale that will allow the people of Scotland an informed choice – ceases to be just my proposal, or that of the SNP.
“It becomes the will of the democratically elected parliament of Scotland.”
The Greens have said they will back the SNP in the vote, which follows a two-day debate, giving Ms Sturgeon a majority.
Ms Sturgeon will say that to “stand in defiance” of this would “shatter beyond repair any notion of the UK as a respectful partnership of equals”.
She will say: “She has time to think again and I hope she does. If her concern is timing then – within reason – I am happy to have that discussion.
“But she should be in no doubt. The will of our parliament must and will prevail.”
Sturgeon: Holyrood’s will ‘must and will prevail’}