Nicola Sturgeon has claimed independence is “within touching distance” ahead of a speech to supporters at a major rally in Glasgow.
She will ask for powers to hold another a referendum on Scotland’s future in the UK shortly after next month’s general election.
However Jeremy Corbyn said a new Scottish independence poll was not “desirable or necessary”.
The Conservatives and the Liberal Democrats also oppose a further vote.
Ms Sturgeon is one of a number of SNP politicians and independence campaigners lined up to speak at the #indyref2020 rally in George Square later.
It will be the first time she has spoken at an independence rally since 2014.
Speaking ahead of the event organised by The National newspaper, the SNP leader focused on the UK-wide election on 12 December.
“This election really is the most important one Scotland has faced in modern times,” she said.
“So much is on the line – people are completely fed up with the mess at Westminster.
“But George Square will be packed as people from all backgrounds join together to demand a better future for Scotland.”
Ms Sturgeon added that independence “really is within touching distance”.
She had faced criticism by some activists for not attending events such as the All Under One Banner march in Edinburgh last month.
However, the first minister did tweet ahead of that march to say she was not able to attend, but would be there “in spirit”.
On Friday the first minister confirmed that she would send a letter “before Christmas” to whoever is in 10 Downing Street, requesting the Scottish Parliament is granted powers to hold another independence referendum.
She has made clear that she wants to hold a poll on the issue next year.
Asked whether she believed Labour would grant the Section 30 order, Ms Sturgeon answered: “Yes”.
“If people in Scotland demonstrate the desire – as I believe they will in this election – for an independence referendum, then I don’t believe Westminster opposition to the principle or to the timetable to that will prove sustainable,” she said.
In response, Jeremy Corbyn said: “Labour does not support independence for Scotland and we do not think another independence referendum is either desirable or necessary.”
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Scottish Conservative leader Jackson Carlaw accused Ms Sturgeon of “not listening”.
He added: “She is obsessed with independence and we must send her a message at this general election. People have had enough of the division and we just want to move on.”
Liberal Democrat general election campaign chairman Alex Cole-Hamilton said: “We are clear on Brexit and clear against the division of independence.”
Others to address the Glasgow rally include Scottish Greens co-leader Patrick Harvie.
“The cause of Scottish independence must be broad and inclusive. Our diversity is our strength,” he said.
“Those people who are still to decide need to be offered a positive, hopeful vision about how we can live in a fair, equal, sustainable country, and why independence will help.”