The find, on the Glendronach prospect north-west of Shetland, has the potential to deliver around one trillion cubic feet of recoverable gas.
French energy giant Total has described the resource as “significant” and is confident it can be developed rapidly using the firm’s existing pipelines and Shetland gas plant.
It is thought the well could have a productive life of ten to 15 years, or perhaps longer.
Arnaud Breuillac, president of exploration and production for the energy company, said: “Glendronach is a significant discovery for Total, which gives us access to additional gas resources in one of our core areas and validates our exploration strategy.
“Located on an emerging play of the prolific West of Shetland area, the discovery can be commercialised quickly and at low cost by leveraging the existing Laggan-Tormore infrastructure.”
The announcement comes soon after it was revealed that the value of Scottish sales for oil and gas rose almost 20 per cent in the past 12 months, despite a fall in production.
Glendronach is operated by Total, which has a 60 per cent interest in the discovery, alongside power firm SSE and chemicals company Ineos, which each have 20 per cent.
The gas will be piped from Shetland to the St Fergus terminal at Peterhead, then fed into the distribution network.
Martin Pibworth, wholesale director for SSE, said: “This discovery represents a major addition to SSE’s recoverable gas resources.
“Gas production assets are a natural complement to SSE’s interests in gas-fired power generation and gas supply to business customers.”
Deirdre Michie, chief executive of the trade association Oil & Gas UK, said: “This is a major discovery by Total, which demonstrates the exciting potential the West of Shetland frontier region holds.”
She said the focus on rapid commercialisation provides “motivation” for investors and industry. She added: “This significant discovery demonstrates that the improved competitiveness of the basin is having positive results.”
Alexander Burnett, Scottish Conservative energy spokesman, said the latest find is proof that the North Sea still has huge potential.
He said: “It’s more important than ever for the Scottish and UK governments to work together to secure the long-term future of the North Sea oil and gas sector.”
But environmentalists say the find is a “disaster” for the climate and the resource should remain untapped.
Dr Richard Dixon, director of Friends of the Earth Scotland, said: “Exploitation of this new gas discovery off the coast of Shetland is incompatible with a country and a world that takes climate action seriously.
“The world cannot afford to burn even a fraction of the fossil fuels we already know about. Fossil fuel firms should not be searching for and exploiting new reserves.
“This summer of extreme weather has shown we are long past the time for business as usual. This gas should stay where is it.
“On the same day the Scottish Government is urged by its own climate advisers to do more to cut emissions, it needs to end further oil and gas exploration in the North Sea.”
Gina Hanrahan, acting head of policy at WWF Scotland, said: “We can’t limit global warming with one hand tied behind our backs.
“To bring down our emissions globally we simply can’t burn most of our existing fossil fuel reserves, let alone new discoveries like this Shetland field. The smart money should be going into clean energy, not risking stranded assets in the North Sea.”