The date, 547 days from today, was revealed to MSPs by the First Minister as he set out the full details of the referendum bill, saying: "I believe it will be the day we take responsibility for our country."
Voters will go to to the polls exactly 100 years since the Irish Home Rule Act was given royal assent, although that legislation was suspended by the onset of the World War 1, and then superseded by a separate bill.
The Referendum Bill: read the full details here
The Scottish Government had previously said only that the ballot would be held in autumn 2014, but there was speculation that the date of October 18 had been pencilled in after an apparent leak to a tabloid paper. However, that would have clashed with the school holidays and the National mod in Inverness.
Having it in September still allows the Yes camp to hope for a feelgood bounce from two major events next year in Scotland: Glasgow’s Commonwealth Games, which runs in the city and at at venues elsewhere from July into August; and the build-up to the Ryder Cup at Gleneagles, where Europe will be defending their crown against the USA from September 26-28.
Two other seminal historic moments which are bound to form part of the independence/unionist narrative in 2014: the 700th anniversary of the Battle of Bannockburn (June 23-24), and the 100
th anniversary of the start of World War 1 (June 28).
Mr Salmond's deputy, Nicola Sturgeon, this morning tweeted an image of her signing the bill, along with the words: "When I joined @thesnp at 16, I never imagined I'd one day put my signature on an #indyref Bill."
She visited the Steel Engineering fabrication plant in Renfrewshire to meet apprentices who have cut and welded a large representation of the date to promote the launch.
The date was unveiled nearly two years after the SNP won an overall majority at Holyrood, allowing it to press ahead with a vote on the party's long-cherished goal of independence.
A Bill paving the way for the referendum confirmed the question: "Should Scotland be an independent country? Yes or No" and spending limits for campaign groups and political parties.
The independent Electoral Commission will act as watchdog ensuring, said Mr Salmond, a contest of "the highest international standards of fairness and transparency".
In a brief speech to MSPs, the First Minister put the case for leaving Britain, arguing that last year Scotland's finances were in a stronger position than the UK's.
He said Scots could remove Trident nuclear missiles from the Clyde and end spending cuts imposed by the Coalition Government at Westminster under independence.
He said the referendum "will be a truly historic day for our nation. The day when the people will decide Scotland’s future."
He immediately faced calls to set out his plans for an independent Scotland.
Scots Labour leader Johann Lamont urged him to bring forward the Government's blueprint for independence - not due until November - adding: "If not the whole country will be asking, 'What's the plan, Alex?'"
In a dig at the long delay between the election and announcement of the referendum date, she said: "If the hand of history is on his shoulder I do wish it had given him a shove and made him get on with it."
She warned Scotland would remain "on pause", with growing problems in the health service and education, until the referendum was decided in 18 months' time.
She added: "The truth about the delay is that if it was held now he would not just lose, he would be routed."
Mr Salmond said that in the ballot the people of Scotland would have a choice.
"Next year the choice facing the people is one of two futures. A No vote means a future of governments we didn't vote for, imposing cuts and policies we didn't support. A Yes vote means a future where we can be absolutely certain, 100% certain, that the people of Scotland will get the government they vote for," he said.
"I believe (September 18) will be the day we take responsibility for our country, when we are able to speak with our own voice, choose our own direction and contribute in our own distinct way."
Leaving the UK and becoming a separate country would give Scotland a "new, more modern relationship with the other nations of the UK" that would be a "true partnership of equals".
He said: "I believe on September 18 the people of Scotland will vote Yes to create a better country than we have now, one we can pass on with pride to the next generation."
Independence will prevent "draconian welfare reforms" from being "imposed" upon Scotland by the Westminster Government, Mr Salmond said.
The Scottish Parliament would try to mitigate the worst affects of changes such as the so-called bedroom tax which will see housing association and council tenants lose some of their benefits if they have spare bedrooms.
"Until we have the full powers of independence we cannot prevent them from being imposed upon the people of Scotland," he said.
"The choice becomes clearer with each passing day: the opportunity to use our vast resources and talent to build a better country, or to continue with a Westminster system that simply isn't working for Scotland."
Other opposition politicians accused Mr Salmond of delay tactics by waiting until now to reveal the proposed date.
Liberal Democrat leader Willie Rennie said: "After all the build-up, this looks like one of those occasions where the trailer is more exciting than the movie.
"If he loses will he join me and others to develop a new consensus for more powers for the Scottish Parliament in the UK?"
Mr Salmond said: "The timetable I have laid out is exactly as we said we are going to do."
"It is true that the referendum Bill gives people substantial notice of when the referendum is going to be held," Mr Salmond said.
"I think that is a good thing. I think we should take it through parliamentary procedures. I think we should have that discussion and debate."
Scottish Conservative leader Ruth Davidson welcomed the clarity brought by the statement, and called for the level of the independence debate to rise beyond "baseless assertions" and "exaggeration".
She said: "The First Minister knows that the people of Scotland have expectations regarding the level of debate. They also demand and desire information they can trust on which to base this most important of decisions."
Green Party co-leader Patrick Harvie, who backs independence, said a No vote could result in the debate being stymied by "various flavours" of further devolution "with very little chance of ever being implemented".