The campaign to keep Scotland in the United Kingdom will be launched under the slogan: "We want the best of both worlds."
Former chancellor Alistair Darling MP will lead a cross-party group calling itself the "Better Together" campaign.
It has taken out pre-launch advertisements in 10 Scottish newspapers telling readers that Scots do not have to choose between a distinctive Scottish Parliament and the strength of the UK - devolution offers both.
Speaking before the launch, Mr Darling told Sky News: "We put the positive case for staying together.
"We are positive about our links with the rest of the United Kingdom - through families and friendships, through trade, and through shared political, economical and cultural institutions."
"We're positive about being a proud nation within a larger state and the far wider range of opportunities of our people that this creates.
"We're positive about all of the identities we share - Scottish, British, European, citizens of the world - and don't see the need to abandon any of them.
"We are part of a social union, underpinned by an economic and political union. All parts mesh together.
"Friends, neighbours, families - across borders - share ties that bind us together.
"What does this mean for us? It means that after centuries of common endeavour we should value those ties that bind us together and celebrate the diversity that exists around us."
Scotland's SNP Government plans to hold a referendum on Scottish independence in the autumn of 2014.
It wants to ask voters the question: "Do you agree that Scotland should be an independent country?"
There has been continued disagreement over the proposed timing of the ballot and on whether or not 16-year-olds are given the vote, in line with the SNP's wish.
The Nationalists' opponents have also called for an independent commission to frame the referendum question; they believe that, in its current form, it encourages a "yes" vote by failing to include mention of an end to the union.
Opinion polls have consistently shown that the majority of Scots favour staying in the union.
The launch of the pro-union campaign comes in the wake of recent polls that indicate a drop in support for Scottish independence.
The arguments on the issue have been well-rehearsed.
Most recently, Mr Darling has focused on SNP plans for a "sterling zone" currency , in which an independent Scotland would keep the pound.
He has described it as "barmy" and warned that it could be blocked by voters in the rest of the United Kingdom.