On Wednesday, Zaghari-Ratcliffe's local UK Member of Parliament Tulip Siddiq tweeted a photo of her on board a plane saying she is now on her way home.
"It's been 6 long years - and I can't believe I can FINALLY share this photo," wrote Siddiq. "Nazanin is now in the air flying away from 6 years of hell in Iran."
UK Foreign Secretary Liz Truss said in a tweet that Zaghari-Ratcliffe and fellow British Iranian national Anoosheh Ashoori "will be reunited with their families later today."
UK Prime Minister Boris Johnson hailed their release as "huge achievements" for British diplomacy. "I pay tribute to the tireless efforts of those who have worked for six years to make today's events possible," Johnson wrote in a tweet.
This comes as Truss announced that the UK had settled a decades-old £400 million ($524 million) debt owed to Iran, which Iran's Foreign Minister Hossein Amir-Abdollahian denied was linked to the prisoner release.
"After highly complex and exhaustive negotiations, the more than 40-year-old debt between the International Military Services and the Ministry of Defense of Iran has now been settled," Truss said in statement to Parliament.
The debt is for undelivered armored vehicles and tanks, originally ordered by Iran but canceled by the UK in response to the Iranian revolution of 1979, according to a research briefing published by the House of Commons Library.
Iran's state-run Press TV said that Zaghari-Ratcliffe had been handed over to the UK government, without providing any further details. The country's semi-official Fars news agency said she was being transferred to Tehran's international airport, Imam Khomenei, with a British negotiating team.
On Wednesday, Hojjat Kermani, Zaghari-Ratcliffe's lawyer, told CNN he did not want to comment on the latest developments for now.
He earlier told Reuters that Zaghari-Ratcliffe and another detained British-Iranian, Anousheh Ashouri, were "on their way to the airport in Tehran to leave Iran."
Mayor of London Sadiq Khan said he was "delighted" that Zaghari-Ratcliffe had been freed from "wrongful imprisonment" in a statement Wednesday.
"Nazanin and her loved ones have shown great courage, strength and steadfastness during what has been an unimaginably difficult time, and I want to pay tribute to all those who have campaigned tirelessly for her release," said Khan. "London looks forward to welcoming her home."
Her husband Richard Ratcliffe said the release of his wife means they can "start being a normal family again."
Speaking to reporters in London, Ratcliffe said he hadn't yet spoken to his wife but that they had exchanged messages on Wednesday.
He said she got picked up by the Iranian Revolutionary Guard at 11:00 a.m. local time (3:30 a.m ET) and that although she "wasn't really allowed to speak" he was aware of her movements.
"Her homecoming is a journey not an arrival. There will be a whole process and hopefully we will look back in years to come and we will be a normal family," Ratcliffe continued.
On Wednesday, a campaign group which pushed for Zaghari-Ratcliffe's release thanked Siddiq, the family's member of parliament, for her work on the case.
"You have made a difference @TulipSiddiq! Thanks for all the amazing support you have given to #FreeNazanin over these 6 long years," the group wrote on Twitter.
Husband's hunger strikes
Zaghari-Ratcliffe was first detained at a Tehran airport in April 2016 following a vacation to see her family with her daughter.
She was accused of working with organizations allegedly attempting to overthrow the Iranian regime and was later convicte