Ed Miliband has promised to hand "crucial" new powers to the Scottish Parliament if he is elected Prime Minister next year.
With less than a year to go to the next General Election, the Labour leader said he was "determined" to bring his party back to power across the UK.
He used a visit to Dundee to announce a new "contract" with the people of Scotland - five key pledges he said Labour would deliver in its first batch of legislation.
Central to that is a commitment to introduce a new Scotland Act to devolve further powers north to Holyrood.
It comes after Labour's devolution commission recommended Scotland get more responsibility over income tax, including the ability to increase the higher rates - along with powers over housing benefit and the work programme.
Mr Miliband said: "We are the people who will give more power to the Scottish Parliament and can have the best of both worlds, which is a Scottish Parliament and the strength and security and social justice that the United Kingdom can bring, if we can elect a Labour government, which is what I am determined to do."
Mr Miliband, who was visiting the Michelin tyre factory, added: "I think the rest of the United Kingdom benefits massively from Scotland's presence. If you think about our historic achievements, whether it is the NHS or the minimum wage or workers' rights, they came about in part because of Scottish figures, the Scottish political movement.
"So I believe the rest of the United Kingdom wants Scotland to stay. I also happen to believe its in Scotland's interests to stay. In the end that's a decision for the people of Scotland."
Mr Miliband's "contract" with Scots also includes a promise to bring in a 50p rate of income tax for top earners - which could affect 14,000 people north of the border - as well as reintroducing the 10p tax band for low paid workers.
Labour would freeze gas and energy prices, and introduce a jobs guarantee for young people who have been out of work for a year or more, offering them a six-month paid position to help get them back into the employment market.
In addition, zero-hours contracts would be banned, with workers being given more rights to demand fixed-hours contracts, a move Labour believes could help at least 90,000 workers in Scotland.
In response, the SNP said Mr Miliband had "nothing to offer" in the debate over Scotland's future, and insisted only independence would guarantee more powers for Holyrood.
MSP Stewart Maxwell said: ""The people of Scotland will not be fooled by Labour's promises of further powers. In 1979 we were promised 'a better form of Devolution' if we voted No - but in reality all we got was 18 years of Tory government."