An 85-year-old Iranian-American citizen, Baquer Namazi, a former head of UNICEF, was released "to seek medical treatment abroad" after being detained in Iran for over six years.
Together with him, his son Siamak Namazi was also released.
This was announced by Stephane Dujarric, spokesman for the UN secretary general, Antonio Guterres.
Namazi was jailed in February 2016 when he went to Iran to free his son, an Iranian-American businessman arrested the year before.
Both had been sentenced to ten years in prison for espionage.
The elder had been exempted from serving his sentence in 2020 but could not leave Iran despite his health problems.
Guterres said he was "grateful that following his appeals to the president of the Islamic Republic, our former colleague Baquer Namazi was authorized to leave Iran to receive medical treatment abroad".
"The Secretary General is also pleased to learn that Baquer Namazi's son Siamak Namazi has been released from detention. We will continue to engage with the Iranian authorities on a number of important issues, including the regional situation, sustainable development and promotion and protection of human rights ", reads the note again.
The United States had pushed for the release of both and two other Americans as part of efforts to revive the 2015 nuclear deal between Iran and Western powers.