Iran and world powers have reached a historic deal under which Tehran will curb its nuclear program in exchange for the easing of economic sanctions, NBC News confirmed early Tuesday.Tehran has been negotiating with the U.S., Britain, France, Germany, Russia and China for years, with diplomats extending a series of deadlines in hopes of arriving at a workable plan.

The deal — reached after marathon overnight negotiations in Vienna — overcame stiff opposition from close U.S. allies Israel and Saudi Arabia, who say Iran cannot be trusted with a nuclear program of any kind.

It involves offering sanctions relief to Tehran only once Iran has achieved agreed upon limitations on its nuclear program.

On Tuesday, the European Union said the final plenary between Iran and the six other countries negotiating — known as the P5+1 — would be held at 10:30 a.m. Vienna time (5:30 a.m. EDT), followed by a press conference.

Next, the agreement faces a vote in Congress, although it is unclear whether Republicans and some Democrats who object to the deal will actually be able to override the decision.

Iran’s moderate President Hassan Rouhani has staked a large share of his political future on a successful outcome of talks, and stands to be one of the biggest winners out of the agreement.