Iranian President Hassan Rouhani said "a new chapter" has begun in his nation's relations with the world.
Beyond the hopeful proclamations from the U.S., Iran and other parties to the talks, there is deep skepticism of the deal among Iranian and U.S. lawmakers. Obama's most pressing task will be holding off efforts by Congress to levy new sanctions on Iran or block his ability to suspend existing ones.
The deal was finalized after more than two weeks of furious diplomacy in Vienna. Negotiators blew through three self-imposed deadlines, with top American and Iranian diplomats both threatening at points to walk away from the talks.
Secretary of State John Kerry, who did most of the bargaining with Iranian Foreign Minister Muhammad Javad Zarif, said persistence paid off. "Believe me, had we been willing to settle for a lesser deal we would have finished this negotiation a long time ago," he told reporters.
The economic benefits for Iran are potentially massive. It stands to receive more than $100 billion in assets frozen overseas, and an end to a European oil embargo and various financial restrictions on Iranian banks.
The breakthrough came after several key compromises.
Iran agreed to the continuation of a UN arms embargo on the country for up to five more years, though it could end earlier if the International Atomic Energy Agency definitively clears Iran of any current work on nuclear weapons. A similar condition was put on UN restrictions on the transfer of ballistic missile technology to Tehran, which could last for up to eight more years, according to diplomats.
Washington had sought to maintain the ban on Iran importing and exporting weapons.
Iran, backed by Russia and China, insisted the embargo had to end as their forces combat regional scourges such as the ISIL.
Another significant agreement will allow UN inspectors to press for visits to Iranian military sites as part of their monitoring duties. However, access isn't guaranteed and could be delayed.
Under the accord, Tehran would have the right to challenge UN requests, and an arbitration board composed of Iran and the six world powers would then decide on the issue. The IAEA also wants the access to complete its investigation of past work by Iran, and the U.S. says Iranian cooperation is needed for all economic sanctions to be lifted.
IAEA chief Yukiya Amano said Tuesday his agency and Iran had signed a "roadmap" to resolve outstanding concerns, hopefully by mid-December.