Nicola Sturgeon's call for a second referendum on independence for Scotland has been formally backed by the Scottish Parliament.
MSPs voted by 69 to 59 in favour of seeking permission for a referendum before the UK leaves the EU.
Ms Sturgeon says the move is needed to allow Scotland to decide what path to follow in the wake of the Brexit vote.
But the UK government has already said it will block a referendum until after the Brexit process has been completed.
Prime Minister Theresa May, who met Ms Sturgeon for talks in Glasgow on Monday, has repeatedly insisted that "now is not the time" for a referendum.
Her Scottish secretary, David Mundell, has said that the timescale could include "the Brexit process, the journey of leaving and people being able to understand what the UK's new relationship with the EU is, so they can make an informed choice if there was ever to be another referendum".
But Ms Sturgeon, the Scottish first minister, said her mandate for another vote was now "beyond question", and warned it would be "democratically indefensible and utterly unsustainable" to attempt to stand in the way.
She told a debate ahead of the Holyrood vote that she was not seeking confrontation with the UK government, and only wanted "sensible discussions".
'Right to choose'
Ms Sturgeon said: "My argument is simply this: when the nature of the change that is made inevitable by Brexit becomes clear, that change should not be imposed upon us, we should have the right to decide the nature of that change.
"The people of Scotland should have the right to choose between Brexit - possibly a very hard Brexit - or becoming an independent country, able to chart our own course and create a true partnership of equals across these islands."
She added: "I hope the UK government will respect the will of this parliament. If it does so, I will enter discussion in good faith and with a willingness to compromise.
"However, if it chooses not to do so I will return to the parliament following the Easter recess to set out the steps that the Scottish government will take to progress the will of parliament."
The two-day debate in the Scottish Parliament started last week but was suspended as news of the terror attack at Westminster emerged.
MSPs were asked to mandate the Scottish government to take forward discussions with the UK government on the details of a section 30 order, which is needed to make a referendum legally binding.
Ms Sturgeon's minority SNP government was backed by the pro-independence Scottish Greens in the vote, with the Conservatives, Labour and Lib Dems opposed.
The first minister is now expected to make the formal request for a section 30 later this week - after Mrs May formally starts the Brexit process on Wednesday by triggering Article 50.
Scottish voters rejected independence by 55% to 45% in a referendum in 2014, but Ms Sturgeon believes the UK voting to leave the EU is a material change in circumstances which means people should again be asked the question.
Analysis by Brian Taylor, BBC Scotland political editor
The first minister's speech featured an oblique warning to the prime minister. Oblique in that the details remain undisclosed.
If the PM worked with the wishes of the Scottish government (and, after tonight's vote, parliament), then there would be co-operation. If not, then she would return after the Easter recess with an alternative approach.
Broadly, what might be involved? A party campaign can be presumed. Motions and debates in Holyrood and Westminster can be taken as read.
And more? Ministers reckon that the UK government may need Holyrood consent and support at sundry points during the Brexit process.
Presumably, said support will be absent or grudging if UK ministers continue with their refusal even to countenance an independence referendum.
Responding to the Holyrood vote, Mr Mundell again insisted that it "simply wouldn't be fair to hold a referendum during the Brexit process" as people would not yet know what the future relationship between the UK and EU will be.
He added: "We are not entering into negotiations on whether there should be another independence referendum during the Brexit process. We don't have a crystal ball as to how long that process will take. We don't recognise, for example, 18 months as being a key point in the journey.
"It will be a journey that will involve the negotiations with the EU, it may be a journey that involves transitional measures, it may be a journey that involves significant implementation time."
Analysis by Prof John Curtice, Strathclyde University
While Theresa May may not want a formal referendum campaign to be going on in the next 18 months, I think, in truth, an informal one is going to start and there is nothing she can do about that.
The argument is going to be whether or not it happens before or after May 2021 (when the next Holyrood election is due).
That will depend, in part, on what the opinion polls say, both about the principles of holding a referendum and also where the question of independence itself stands. And also to what extent Brexit is, or is not, seen to be a successful process.
All of this, undoubtedly, is extremely uncertain.
Scottish Conservative leader Ruth Davidson said the decision to press ahead with an "unwanted second referendum" would only add to the uncertainty facing Scotland.
She added: "It provides yet more evidence that this SNP government has given up on its stated priority to focus on education, and is now intent of running an endless campaign for another vote that people don't want."
Scottish Labour leader Kezia Dugdale said Scotland had voted "decisively" to remain in the UK in the 2014 referendum, and warned the first minister: "We are divided enough, do not divide us again."
But Ross Greer of the Scottish Greens said: "It should be our responsibility, as those elected by the people of Scotland, to fight for their right to choose their own future."
Lib Dem leader Willie Rennie said: "Scottish Liberal Democrats stood on a manifesto to oppose a divisive referendum and we will continue to do that".