The temporarily release delighted her family, with husband Richard Ratcliffe telling LBC, he was "very happy" to see her again.
She is now with her family in Damavand and has been reunited with her four-year-old daughter, Gabriella.
Although the initial release is for three days her lawyer is hopeful that this can be extended, her husband said.
Boris Johnson told a parliamentary committee that Mrs Zaghari Ratcliffe was working in Tehran training journalists
The British-Iranian citizen has been detained by Iranian authorities since 2016 for allegedly seeking to overthrow the government. She was also required to sign a document stating that she would return to the prison after the furlough period ends.
The British arm of Amnesty International also celebrated her temporary release as an "amazing news".
The new foreign secretary Jeremy Hunt tweeted today to say that Mrs Zaghari-Ratcliffe must be "PERMANENTLY released, ' and that 'every effort will continue" to achieve this.
According to the Free Nazanin campaign, Zaghari-Ratcliffe's father had asked that she be given furlough for a month (her legal entitlement is now 29 days) so that she and Gabriella could rebuild their relationship.
'This was a very happy surprise after a number of false dawns recently, which had been increasingly unsettling'.
Consequently, authorities in Tehran used the comment as evidence for her imprisonment. Her daughter was two at the time- her passport was taken when her mother was imprisoned, and she has remained with family in Iran since.
Johnson later clarified his remarks, saying it was clear that she was only on holiday.
Bail for her temporary release was set at one billion rials ($23,800), with her family's home in Tehran used as collateral, the campaign said. "Nazanin is innocent. She has a 4-year-old daughter Gabriella".
"I think the very next steps are to see if we can extend the furlough beyond three days", he said.