Behnam Irani was detained for religious services conducted at a house church for around 300 people.
It is thought that the 43-year-old, jailed for sharing his faith, is in poor health following his ordeal in Ghezal Hesar prison, reputedly one of the toughest jails in Iran.
Andrew Boyd from Release International, a charity supporting persecuted Christians, told Premier's News Hour he is thrilled Irani has been released.
He said: "It's an absolute joy to hear that he's been released, there's no leniency involved in this, he's been released dead on time by the Iranian authorities.
"Release's partners in Iran say there's something like 200 other prisoners who remain in jail in Iran, because of their faith."
Iran:
Population: 80 million, 475,000 Christians
Main Religion: Islam
Government: Islamic republic
World Watch List Rank: 9
Source of Persecution: Islamic extremism
He told Premier that the Christian leader has been ill in prison: "We understand he's in good spirits but in poor health, he was put in solitary confinement for a time and then he was shifted into a cell with some of the most violent prisoners, not even enough room to lie down.
"He was warned that he wouldn't get out of jail alive... he's been vomiting blood, he's been severely beaten."
Pastor Irani is now expected to be reunited with his wife, Kristina, an Armenian, and his two children, 11 year old Rebecca, and his younger son, Adriel.
Iran ranks at number nine on Open Doors World Watch List of Christian persecution throughout the world and Release is pushing for the release of more prisoners of faith.
Listen to Premier's Alex Williams speak to Andrew Boyd here:
