The Scottish parliament backed Nicola Sturgeon’s call for the powers to hold a second independence referendum, which British prime minister Theresa May has already said she will not allow until Brexit has been negotiated.
MSPs voted 69-59 to mandate the first minister to seek permission from the UK government for a ballot to be held between autumn 2018 and spring 2019.
Ms Sturgeon’s minority government won the vote following an extended debate thanks to support from the Scottish Greens.
Ms May has already said she will block another referendum while the Brexit process takes place, stating “now is not the time”.
The two-day debate started last week but was suspended on Wednesday as news of the terror attack at Westminster emerged.
The vote came ahead of the process of Britain leaving the EU being formally triggered by Ms May today.
Ms Sturgeon has insisted her referendum timetable would allow Scottish voters to make a choice when terms of the Brexit deal become clear and before it is “too late to choose our own course”.
Speaking before the leaders’ meeting on Monday, Ms May said her position will not change, arguing that a vote within Ms Sturgeon’s proposed time frame would be unfair to voters and come at a time when the focus should be on securing the best Brexit deal for the whole of the UK.
Ms Sturgeon said: “It is now the will of Scotland’s democratically elected national parliament that discussions should begin with the UK government to enable an independence referendum to be held.
“Today’s vote must now be respected. The mandate for a referendum is beyond question, and it would be democratically indefensible — and utterly unsustainable — to attempt to stand in the way of it.
“We will now act on the mandate given to us by parliament by making a formal approach to the UK government within the next few days, after Article 50 has been triggered.
“This is, first and foremost, about giving the people of Scotland a choice on this country’s future.
“The prime minister says that now is not the time for a referendum. I agree with that, which is why I have indicated a time scale no earlier than 18 months from now, when the terms of Brexit are clear — something the PM has now indicated she agrees with.
“It is up to the UK government to now make clear when they consider a referendum would be appropriate.”
UK Scottish secretary David Mundell told BBC Scotland: “We won’t be entering into any negotiations at all until the Brexit process is complete.
"Now’s the time for the Scottish government to come together with the UK government, work together to get the best possible deal for the UK, and that will mean for Scotland as we leave the EU.”
A British government spokeswoman said: “The prime minister has been clear that now is not the time for an independence referendum, and we will not be entering into negotiations on the Scottish government’s proposal.
“At this point, all our focus should be on our negotiations with the European Union, making sure we get the right deal for the whole of the UK.
“It would be unfair to the people of Scotland to ask them to make a crucial decision without the necessary information about our future relationship with Europe, or what an independent Scotland would look like.
“We have been joined together as one country for more than 300 years. We’ve worked together, we’ve prospered together, we’ve fought wars together, and we have a bright future. At this crucial time we should be working together, not pulling apart.”
Scottish Conservative leader Ruth Davidson said the decision to press ahead with another referendum is “deeply regrettable”.
She said: “We have made it clear: Now is not the time to go back to another divisive referendum. Not when there is no public support for one.
"Not when the SNP said the last referendum would be once in a generation. Not when we have no clear picture as to what either Brexit or independence will look like.
“We will continue to oppose a second referendum every step of the way. The majority of people in Scotland do not want it and the SNP does not have a clear mandate to pursue it.”