Nicola Sturgeon says she will give Scots a "real choice" between Brexit and leaving the UK in a second vote on independence.
The First Minister confirmed she is to seek the approval of the Scottish Parliament next week to start negotiations with the UK Government on staging a fresh referendum.
That could see a second independence vote take place as early as autumn 2018 - just four years on from when Scots voted by 55pc to 45pc to stay part of the United Kingdom.
It comes after nearly two-thirds (62pc) of Scots opted to stay in the European Union, but the UK as a whole voted for Brexit.
Within hours of that result being known, the SNP leader said another referendum was "highly likely".
Speaking at her official residence, Bute House in Edinburgh, the First Minister said: "I will now take the steps necessary to make sure that Scotland will have a choice at the end of this process - a choice of whether to follow the UK to a hard Brexit or to become an independent country, able to secure a real partnership of equals with the rest of the UK and our own relationship with Europe."
Ms Sturgeon said she would go to Holyrood next week and "seek the authority of the Scottish Parliament to agree with the UK Government the details of a section 30 order - the procedure that will enable the Scottish Parliament to legislate for an independence referendum".
She added: "The timing of the Brexit negotiations are not within the control of the Scottish Government, however we must plan on the basis of what we do know now.
"On the timetable set out by the Prime Minister the shape of the Brexit deal will become clear in the autumn of next year, ahead of ratification votes by other EU countries.
"That is, therefore, the earliest point at which a referendum would be appropriate."
The First Minister said: "If Scotland is to have a real choice, when the terms of Brexit are known but before it is too late to choose our own course, then that choice must be offered between the autumn of next year 2018 and the spring of 2019."
With the UK having voted to leave the EU in June 2016, Ms Sturgeon said that change was now "inevitable".
While she added "the option of 'no change' is no longer available", she insisted Scots could "still decide the nature of change".
Ms Sturgeon stated: "Having Scotland's referendum - at a time when the terms of Brexit are known - will give the Scottish people a choice about the kind of change we want.
"It must be a choice for all of us."
She continued: "If I ruled out a referendum, I would be deciding - completely unilaterally - that Scotland will follow the UK to a hard Brexit come what may, no matter how damaging to our economy and our society it turns out to be.
"That should not be the decision of just one politician - not even the First Minister.
"By taking the steps I have set out today, I am ensuring that Scotland's future will be decided not just by me or the Scottish Government.
"It will be decided by the people of Scotland.
"It will be Scotland's choice. And I trust the people to make that choice."
Ms Sturgeon had hoped Scotland would be able to remain in the European single market, even after the rest of the UK leaves the trading bloc.
But she said these "compromise" proposals had been met with a "brick wall of intransigence" from the UK Government.
A paper published by the Scottish Government in December also insisted that significant new powers should be transferred north as a result of Brexit.
The Tories, however, have said negotiations must take place to determine where best power should lie after the UK exits the EU.
Prime Minister Theresa May told the Scottish Conservative conference in February that powers "'must sit at the right level to ensure our United Kingdom can operate effectively''.
Ms Sturgeon hit out at the Prime Minister, saying: "UK membership of the single market was ruled out with no prior consultation with the Scottish Government or indeed with the other devolved administrations - leaving us facing not just Brexit, but a hard Brexit.
"There has been talk of special deals for the car industry and others, but a point blank refusal to discuss in any meaningful way a differential approach for Scotland.
"And far from any prospect of significant new powers for the Scottish Parliament, the UK Government is becoming ever more assertive in its intention to muscle in on the powers we already have."
The First Minister said: "The language of partnership has gone, completely."
She added: "There should be little doubt about this - if Scotland can be ignored on an issue as important as our membership of the EU and the single market, then it is clear that our voice and our interests can be ignored at any time and on any issue.
"That cannot be a secure basis on which to build a better Scotland."