The battle to keep the UK together will be won through Labour's plans to restore social justice to the entire country, Ed Miliband will declare.
With the independence referendum taking place in six months, the Labour leader will use his key address to the party's Scottish conference to insist that the UK is "better together".
He will set out his vision to build prosperity across the UK and create a "country that is more just, more equal, more fair".
Mr Miliband will say he "passionately" believes that Scotland should stay in the UK, and will invoke the memory of former Labour leader John Smith, who died 20 years ago, by calling on the party to "honour his legacy by winning the fight for Scotland to remain in the United Kingdom".
The Labour leader will tell the party activists: "This is no ordinary time and no ordinary conference for reasons we all know, because in 180 days Scotland will determine its future. It is Scotland's decision - and Scotland's alone. But everyone in this Labour Party knows we're better together.
"When we're in need, we don't ask whether we are Scottish, English, Welsh or Northern Irish, we look after each other. And, in the same way, we will build prosperity for the future and for every part of the United Kingdom in a race to the top by creating those good, high-paying jobs that people should expect."
He will highlight Labour proposals to freeze energy bills, tax bankers' bonuses to guarantee jobs for young people who have been out of work for more than 12 months, and reintroduce the 50p top rate of tax for those earning £150,000 a year or more.
Mr Miliband, who visited the Rosyth dockyard to see how work on a new aircraft carrier for the Royal Navy is progressing, will also set out a vision of future Labour governments at Holyrood and Westminster working together and "never resting until we have built the more just and equal society that every part of the United Kingdom should be".
He will tell the Scottish Labour conference in Perth: "John Smith was a man who passionately believed in social justice in Scotland - and in the United Kingdom. Twenty years on, that flame of social justice still burns. And we can honour his legacy by winning the fight for Scotland to remain in the United Kingdom."
He will also warn of the possible consequences of a Yes vote in the independence referendum, to be held on September 18.
Mr Miliband will say: "If Scotland was to go independent, it would be a race to the bottom not just on tax rates, but on wage rates, on terms and conditions, on zero-hours contracts, on taking on the energy companies, on reforming the banks. Those who can afford it will be paying less, while hard-working families across Scotland will pay more and see their services suffer.
"Alex Salmond, who claims to be a great social democrat, would end up running the same race to the bottom that the Tories have embarked upon. The SNP talk about social justice but they can't build it - because they can't be narrow nationalists and serve social justice at the same time."
The conference comes just days after Labour set out its plans to extend devolution in the event of a No vote in the referendum.
It proposes giving Holyrood the power to vary tax rates by up to 15p in the pound, giving Scotland control of three quarters of the 20p basic rate of income tax. In addition MSPs would also get powers to increase the higher rates of income tax.
Mr Miliband will argue these changes would allow for greater fairness in income tax while preventing a race to the bottom in the rates that people pay.
He will say: "There are millions of people across every part of our country who want a better future for all our young people; who say it is just wrong that so many people in work find themselves in poverty, who want to be part of a country that is more just, more equal, more fair.
"Let's rebuild all of our country in the cause of social justice. Together, not alone; as neighbours on this island, not as strangers; as friends, not as competitors; in a race to the top, not to the bottom."
The SNP pointed to new Panelbase poll figures published on the eve of the conference, which it said show that 45% of people in Scotland believe that Labour has been damaged by being associated with the Conservatives in the No campaign. Some 24% said they do not believe the party has been damaged, according to the figures published by Newsnet Scotland.
It follows a previous Panelbase poll last month, the SNP said, which found that 30% of people in Scotland are less likely to vote Labour as a result of shadow chancellor Ed Balls supporting Chancellor George Osborne in saying that Westminster would not agree to a currency union with an independent Scotland. Seven per cent said they were more likely to vote Labour as a result.
SNP Westminster leader Angus Robertson MP said: "Their alliance with the Tories has backfired badly on the Labour Party - just as George Osborne's 'sermon on the pound' backfired on the No campaign."
He continued: "A Yes vote in September is about achieving the powers to build a fair society and prosperous economy in Scotland - and having relationship of friendship and equality with the rest of the UK. It is a positive vision, which is already attracting the support of over a quarter of Labour voters - and the gap between Yes and No is now down to just five points.
"Labour, by contrast, have chosen to stand with the Tories instead of standing up for Scotland - and are paying a heavy price for that foolish decision."