Chancellor Philip Hammond made the pledge during a speech to the Conservative Party conference in Birmingham on Monday (3 October).
Previously, the government had agreed to continue funding only for EU projects signed before the Chancellor's Autumn Statement, which is expected on 23 November.
But Mr Hammond said: "I can offer some additional certainty to British businesses and other organisations bidding to receive EU funding while we're still a member."
See also: Government makes Brexit funding pledge
He added: "The Treasury will offer a guarantee to bidders whose projects meet UK priorities and value for money criteria that if they secure multi-year EU funding before we exit, we will guarantee those payments after Britain has left the EU."
Rural organisations have welcomed the pledge.
They also welcomed inclusion in the Chancellor's announcement of a commitment to structural growth funds, which play an important role in diversifying rural economies.
Country Land and Business Association president Ross Murray said: "We have been calling for Government to make these commitments to the countryside and the environment.
"This is a crucial step in the transition to a strong post-Brexit future both for the environment and for rural businesses.
"EU funded schemes are vitally important to driving investment in our rural economy and delivering environmental benefits such as creating habitats for wildlife and reducing flood risk."
Mr Murray said the chancellor's announcement had made clear that successful EU Countryside Stewardship scheme applications would now be funded until the contract completes.
Agreements under the Countryside Stewardship scheme usually run for five years.
Mr Murray said landowners and farmers could now apply to deliver this type of environmental work with the confidence that the agreement would be honoured until its completion.