Reopening the Russian market to British beef and lamb could be worth £80 million over the next three years, the Government has said.
The estimate came as Russia was poised to lift its ban on imported British meat following concerns about the cattle disease BSE.
Controls are now so tight that the disease has virtually disappeared in the UK, the Department for Environment, Farming and Rural Affairs (Defra) said.
The move will be a boon for livestock farmers in Devon and Cornwall, which play a key role in the region's economy.
Environment Secretary Owen Paterson said: "British food is recognised around the world for using quality ingredients, for rigorous production standards, and for reliable traceability.
"This deal is further evidence of international confidence in what British producers have to offer.
"Our food exports are booming, recently topping £18 billion a year, and this Government is doing all it can to open up markets abroad."
The agreement with Russia is another export success following the £50 million agreement to export British pork to China which Defra helped to secure in May this year.
The UK Government expects official written confirmation, and full details of the deal from Russian officials within the next few days.
Food and farming is worth £89 billion to the UK economy and employs 3.5 million people.
Last year UK food and drink exports increased by 9% to £18.2 billion, marking the seventh consecutive year of record growth.
Former farmer Neil Parish, Conservative MP for Tiverton and Honiton, welcomed the development.
He said: "It gives us another export market for different joints."