The Cornish have been recognised as a national minority under the Framework Convention, affording them the same protections as the Welsh, Scottish and the Irish.
Those who have pushed for Cornwall to be fully recognised under European rules for the protection of national minorities welcomed the announcement in the old county town of Bodmin by Danny Alexander, chief secretary to the treasury, as "a proud day for Cornwall".
Dick Cole, leader of Cornish independence party Mebyon Kernow, said: "This is a fantastic development. A lot of people have been working for many years to get Cornwall the recognition other Celtic people of the UK already receive.
"The detail is still to come out on what this might mean, but make no mistake that this is a proud day for Cornwall."
The decision puts the Cornish on a par with the Welsh, Scottish and Irish
The announcement means government departments and public bodies will now be required to take Cornwall's views into account when making decisions.
Campaigners have taken their message to Westminster in recent years after concerns policies affecting them were being made from Whitehall without their consideration.
Half a million people signed a petition, opposing 2012's controversial "pasty tax", while thousands marched through Cornwall and in Westminster in an ultimately successful effort to get the Government to reverse plans imposing VAT on hot Cornish pasties.
The full details of any economic benefit borne from Cornwall's inclusion in the convention are still unclear, though it is billed as helping strengthen the Cornish brand, as well as recognise the distinctiveness of the Cornish.
Independent Cornwall Councillor Bert Biscoe, who worked on the campaign, said: "I very much welcome that the Cornish as a group can stand equally beside all other groups in British society."
Fellow campaigner and comedian Edward Rowe, also known as the Kernow King, added: "This is obviously great news for the people of Cornwall.
"I think there is always going to be a certain degree of pessimism when politicians are involved - are they going to be chasing votes, for example.
"But it is great for Cornwall to get the recognition for its culture and heritage that it deserves."