Refusal by Britain's prime minister to discuss an independence referendum would "shatter beyond repair" the United Kingdom's constitutional structure, Nicola Sturgeon told her Scottish National Party.
Sturgeon, Scotland's First Minister, pledged to press on with plans to hold a new Scottish referendum as announced earlier this week, deepening a standoff with the UK government.
Party faithful cheered, clapped and leapt to their feet.
Sturgeon expects to get authorisation from the devolved Scottish parliament on Wednesday to seek the terms for a new secession vote, aiming for a date once the terms for Brexit are clear but before Britain leaves the EU.
"To stand in defiance of (Scottish parliamentary authorisation) would be for the prime minister to shatter beyond repair any notion of the UK as a respectful partnership of equals," Sturgeon said.
"Scotland's future will be in Scotland's hands."
Under the UK's constitutional arrangements, Britain's parliament needs to sign off on any legally binding vote in Scotland. Prime Minister Theresa May told Sturgeon this week that "now is not the time" for a new choice on independence as divorce talks between the world's fifth-largest economy and its erstwhile EU partners get under way.
Britain is expected to trigger Article 50 of the EU's Lisbon Treaty within days
Although May did not deny a vote outright, Scottish nationalists predict her words could build support for secession because she could be seen as telling Scotland what to do.
"(May) 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," Sturgeon said.
Britain is expected to trigger Article 50 of the EU's Lisbon Treaty within days and start the complex Brexit procedure.
Last June's vote to leave the EU has shaken the ties of the United Kingdom's four nations. England, the most populous, and Wales voted to leave while the Scots and Northern Irish wanted to keep their EU membership.
May's Conservatives, now the second biggest party in Scotland's parliament, called Sturgeon's speech disappointing and negative.
Scottish Conservative deputy leader Jack Carlaw accused her of "pursuing her own narrow agenda to the detriment and against the wishes of ordinary Scots".
The Scottish Labour Party said Sturgeon failed to mention poverty once, but mentioned independence 13 times.
In her speech, Sturgeon contrasted an image of an open and progressive Scotland against May's goal of limiting immigration across the UK.
"Scotland isn't full up. If you are as appalled as we are at the path this Westminster government is taking, come and join us," she said.
A ComRes opinion poll for the Sunday Mirror newspaper, published on Saturday but conducted before Sturgeon's speech, showed 59 percent of Britons think May should insist that a Scottish independence referendum should take place only after Britain leaves the EU.