Addressing a rally in Glasgow, Mr Brown said that Scottish values can best be realised as part of the UK and that Britain is strongest when pooling its resources together, citing the examples of the NHS, mining, shipbuilding and other core industries.
But Scottish nationalists have dismissed his claim that taxes would have to rise to fund its welfare plans if the country was granted independence.
Former prime minister Gordon Brown will speak today at the launch of a distinct Labour campaign to keep Scotland in the United Kingdom.
The Kirkcaldy and Cowdenbeath MP will be in Glasgow to help unveil the United with Labour drive, which distances the party from Tory and Liberal Democrat colleagues in the pro-Union Better Together movement.
Scottish party leader Johann Lamont and her deputy, the MP Anas Sarwar, will also take part in setting out a "different view" of Scotland's future at the event in the Emirates Arena.