Thousands of independence supporters have heard Nicola Sturgeon call for “Scotland’s future to be put into Scotland’s hands”.
The first minister told a major rally in Glasgow the time would come to break away from the “chaos of Westminster” in a second independence poll next year.
Labour leader Jeremy Corbyn has said a new Scottish independence referendum was not “desirable or necessary”.
The Conservatives and the Liberal Democrats also oppose a further vote.
Ms Sturgeon was one of a number of SNP politicians and independence campaigners to speak at the #indyref2020 rally in George Square.
The event prompted a counter demonstration by dozens of unionist supporters who waved flags and blew whistles as supporters of Scottish independence gathered.
The SNP leader focused on the UK-wide election on 12 December at the event, which was organised by The National newspaper.
She has made it clear that she wants to hold a poll on the issue next year and said the general election was a “crossroads moment” for Scotland.
Ms Sturgeon told the pro-indy crowds: “Over the next few weeks, it is our job to convince everyone we know to come out on December the 12th and send the biggest, loudest most resounding message to Westminster.
“That it is time for Scotland to choose our own future. It is time for Scotland to be an independent country.
“An independent country that will be the best of friends and family with our neighbours across the British Isles, across Europe and across the world.”
The first minister told the crowd the general election was “the most important election for Scotland in our lifetimes”.
“The future of our country is on the line,” she said. “And there is no doubt whatsoever that Scotland stands at a crossroads moment.”
There were boos from the audience when she claimed a victory for Boris Johnson in the election would result in “a future where Scotland gets ripped out of our European family of nations against our will, a future where the UK turns in on itself, a future of a hostile environment for migrants”.
Instead, she said, there was “a much better alternative”.
Ms Sturgeon said: “That alternative is not a UK Labour government that can’t event make up its mind where it stands on the question of Brexit.”
The first minister’s speech came after she 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.
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 only a Labour government would be able to boost Scotland’s economy and see “the levels of poverty in Scotland, particularly in the big cities of Glasgow, Edinburgh and Dundee, being reduced”.
He added: “Scottish independence would mean a massive gap between what Scotland raises in taxation and what the Scottish people need at the present time.
“I think the much better option is a Labour government for the whole of the UK.”
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The Tories criticised Nicola Sturgeon for prioritising indyref2 “above all else”.
Scottish Conservative MSP for Glasgow, Annie Wells, said: “While Nicola Sturgeon is banging on about indyref2, I’m out talking to people about the state of their local schools, the drug deaths crisis and violent crime taking over our streets, and the problems at the Queen Elizabeth Hospital.
“Instead of tackling the day-to-day things that Glaswegians care about, Nicola Sturgeon is headlining a nationalist rally.
“So this election is about stopping Nicola Sturgeon from dividing our communities all over again, and only a vote for the Scottish Conservatives will do that.”