David Cameron arrived at the Scottish Government headquarters at St Andrews House in Scotland's capital this afternoon where he was greeted by First Minister Alex Salmond.
The pair shook hands and had a short conversation before posing for photographs alongside Deputy First Minister Nicola Sturgeon and Scottish Secretary Michael Moore.
The deal, which has been dubbed "The Edinburgh Agreement", follows months of negotiations about the ballot, expected to be held in autumn 2014.
Private meetings between the two governments have covered contentious issues about the question on the paper, expected to be limited to a single Yes-No option.
Proposals for a second question on further devolution, short of independence, were firmly opposed by the UK Government.
The referendum is expected to be open to 16 and 17-year-olds, as supported by Mr Salmond's Nationalists.
Negotiations between the governments have been led by Ms Sturgeon and Mr Moore.
Speaking before today's meeting, Ms Sturgeon denied the Scottish Government had been out-negotiated because it had failed to secure a "devo-max" second question on the ballot paper.
She said: "We have never said we wanted a second question on the ballot paper.
"What we did say was that option shouldn't be ruled out prematurely; it would have been better left to the Scottish Parliament to decide that.
"But in any negotiation there has to be compromise. Both sides have compromised but overall I'm very satisfied that we have a deal that guarantees a referendum made in Scotland."
Mr Moore said people would have to weigh up whether it is better to remain part of the Union.
"The opportunities in continuing to be part of the United Kingdom are strong," he said.
"Our place in the world - we have much more clout as part of the UK at the top table at the United Nations and Nato, in the European Union, we've got much greater security as part of an economy, the fourth largest defence spender in the world, lots of jobs dependent on that .
"I think these are the issues that people are going to focus on and that will be much more powerful than an uncertain prospect."
Today's landmark event will determine a technical measure known as a Section 30, which passes power from Westminster to Holyrood to legislate on the referendum.
Mr Cameron has pledged that keeping the United Kingdom together is his number one priority.
"This marks the beginning of an important chapter in Scotland's story and allows the real debate to begin," he said.
"It paves the way so that the biggest question of all can be settled: a separate Scotland or a United Kingdom? I will be making a very positive argument for our United Kingdom."
Mr Salmond secured a mandate to hold the referendum by winning an unprecedented majority with his Scottish National Party at Holyrood last year.
He said: "The agreement will see Scotland take an important step toward independence, and the means to create a fairer and more prosperous Scotland. I look forward to working positively for a yes vote in 2014."
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