Devolving power to Cornwall has become Liberal Democrat party policy.
Delegates at the party's spring conference in York voted to allow Cornwall to create a law-making assembly.
The Devolution Enabling Act would also allow other areas with a population of more than a million to wrestle control from Whitehall.
The establishment of a Cornish Assembly akin to devolved governments in Wales and Scotland has been a long-held ambition among many in the Duchy.
Ten years ago, a 50,000-name petition has handed to Downing Street calling for a Cornish Assembly.
But even though it becomes party policy, it would not automatically became Government policy in the current or any future coalition.
For example, abolishing tuition fees remains the party's long-term goal despite the Lib Dems increasing the charge to £9,000 in coalition with the Conservatives.
And the Cornish nationalist party Mebyon Kernow has questioned the party's commitment, arguing it has "jumped on the bandwagon" ahead of a general election.
An assembly would be further than the current Government wants to go under its plan to de-centralise power through a series of "deals", with Cornwall among the next in line.
North Cornwall MP Dan Rogerson, also a Government minister, introduced a doomed Private Members' Bill in 2009 to give the area greater control over its own affairs.
He said: "Bringing more powers and decision making to Cornwall will give local people a greater say over the needs, pressures and concerns that they have on issues like schools, jobs, housing, healthcare and public transport.
"Making devolution to Cornwall a national Lib Dem policy will help the Liberal Democrats deliver for Cornwall in Government and in any negotiations after the 2015 General Election."
Councillor Alex Folkes, deputy leader of the Lib Dems on Cornwall Council, said: "We believe that we can do better cheaper if more powers and responsibilities are handed down from Whitehall and if we are able to work more closely with the health service and other public sector organisations.
"Far too often we are told what to do by Eric Pickles.
"We believe that the people of Cornwall know what is right for Cornwall better than a minister sitting behind a desk in Whitehall.
"The vote is a major step forward in our campaign to remove the shackles and unleash Cornwall's potential."
Cornwall peer and former MP Lord Paul Tyler said: "This policy motion links Liberal Democrat ideals with our practical experience in government, creating a package of measures which are deliverable within the next parliamentary cycle.
"Liberal Democrats are building a stronger economy and a fairer society. Vital to this vision is a state in which government is radically decentralised from London."
Two years ago, two Cornwall Conservative MPs – George Eustice and Sarah Newton – said the campaign for a devolved Cornish Assembly should be ditched as being separate from the rest of the UK would be damaging.
They said at the time: "Instead of clinging to this defunct 1990s devolution agenda, Cornwall must embrace a forward-looking approach.
"This should be less about paying for more politicians in a costly assembly and more about giving those councillors we already have a greater say."