The SNP leader confirmed that she will seek the legal power from the UK Government by the end of the year to stage a repeat of the 2014 vote on leaving the UK.
The union was branded “unsustainable” over the chaos of Brexit by Ms Sturgeon, in her flagship address to her party’s Autumn conference in Aberdeen earlier.
She added: “Its time is coming to an end.”
But the claims were rejected by her pro-union opponents who warned independence will be divisive and mean fresh austerity and tax rises for Scots.
The SNP leader also fired the opening salvo in the 2021 Holyrood election as she unveiled radical new police powers to remove domestic abusers from family homes and proposals to extend state childcare into the Summer holidays.
In a 45-minute speech dominated by independence Ms Sturgeon insisted that she has a “duty” to stage a second referendum next year to give Scots an alternative to the Brexit chaos.
“My call is that the referendum must happen next year,” she added.
“And we are getting ready. By the new year, we will have completed our legislative preparations.
“We are already working to update the independence prospectus.
“And I can confirm today that before the end of this year, I will demand the transfer of power that puts the legality of a referendum beyond any doubt.
“And when I do, the question should not be to the SNP – what will we do if Westminster refuses?
“The question should be demanded of the Westminster parties – what gives you any right to deny people in Scotland our ability to choose our own future?”
The Edinburgh agreement
Westminster has control over the constitution and agreement must struck to transfer power to Holyrood to stage such a vote, similar to the Edinburgh Agreement reached between Alex Salmond and David Cameron in 2012
But this has been refused by Boris Johnson with the Queen’s Speech at Westminster this week effectively rejecting another referendum.
It prompted one leading Scottish Government minister, constitution secretary Mike Russell, to warn this week that a court challenge to secure Scotland’s right to stage a second referendum “cannot be ruled out.”
But the First Minister insisted yesterday that the problem is the current constitutional set-up.
She said: “That problem is the Westminster political union. For Scotland, Brexit shows that the Westminster system is broken.
“And it is broken utterly beyond repair.”
Ms Sturgeon insisted her government had a “cast-iron mandate for an independence referendum”.
She added: “That fact is beyond doubt.
“But we don’t just have a right to offer the people of Scotland a choice over their future. In the circumstances now Scotland faces, we have a duty to do so.
“And it is what we intend to do.”
The fallout of the 2016 Brexit referendum, which saw Scots vote to remain in the UK, was branded a “disaster” by Ms Sturgeon.
She added: “Whatever happens over the next few weeks it will continue to dominate Westminster for years to come. There is no sense in which it will be ‘done’.
“We don’t yet know whether the UK will leave with a deal or without. But we do know that neither of these outcomes is in Scotland’s interests.”
While she said a no-deal Brexit would be “unthinkable” she added that “a deal of the type Boris Johnson is proposing would not be much better”.
The First Minister said: “His plans would take Scotland out of the EU, out of the single market and out of the customs union.”
“Let me make this absolutely clear today, SNP MPs will not vote for that - not now, not ever.”
With a general election widely expected in the coming months Ms Sturgeon said it “can’t some soon enough.”
She added: “When it does our message will be clear, simple and unambiguous - vote SNP to demand independence and secure Scotland’s right to choose.
Ms Sturgeon said: “Some polls suggest that an election might result in a hung parliament.
“The SNP will never put the Tories into power.
“But I have a message for any Westminster party that wants SNP support.
“If you don’t respect Scotland’s right to choose our own future at a time of our own choosing, don’t even bother picking up the phone.”
Tory interim leader Jackson Carlaw said the speech showed that Ms Sturgeon’s priorities were not domestic issues her Government has responsibility for.
“Nicola Sturgeon wants to be judged on health and education, yet she couldn’t spare a single sentence for either during this lengthy and divisive speech,” he said.
“Instead, she simply wanted to get through what was a potentially hostile conference with a series of vacuous promises which will never be kept, and throw some red meat to the hardliners.
He added: “When she does demand the powers to hold a second unwanted and divisive referendum, the answer should be an unequivocal no.”
Liberal Democrat leader Willie Rennie warned independence would mean “cuts and tax rises.”
He added: “Independence will be bad for Scotland just like Brexit because breaking up long term economic partnerships is very hard to do.
Pamela Nash, chief executive of Scotland in Union, added: “This was a speech full of nationalist rhetoric with no answers about the catastrophic impact of breaking up the UK. Nicola Sturgeon’s obsession with dividing communities is clear for all to see.”