An interim agreement to curb Iran's nuclear programme will come in effect on 20 January.
The International Atomic Energy Agency is to make regular inspections of Iran's nuclear facilities and some international sanctions on Tehran will be eased.
The Iranian Foreign Ministry and the European Union made the announcement on Sunday in Geneva.
Five permanent members of the UN Security Council - Britain China, France, Russia, the United States plus Germany conducted the talks with Iran.
Under the terms of the deal, Iran has agreed to halt enrichment of uranium above 5% purity and "neutralise" its stockpile of near-20%-enriched uranium.
In return, the first $US550 million instalment of $US4.2 billion in frozen assets will be released early next month. Some restrictions on trade will also be lifted.
A preliminary agreement was reached in Geneva on 24 November. The latest deal is for six months.
The West accuses Iran of seeking nuclear weapons, but Tehran has consistently denied that.
US President Barack Obama welcomed the announcement, but said more work was needed to strike a long-term deal. He threatened new sanctions if there was a breach.
