According to reports, the resignation was based on disappointment over the ministers proposed to join the new government. At that time, Zarif had been appointed as the vice president of the newly elected president Masoud Pezeshkian just two weeks earlier.
Why he now chooses to return is not entirely clear.
Zarif, Iran's foreign minister between 2013 and 2021 under President Hassan Rohani, was involved in negotiating the international nuclear energy agreement in 2015. He has also been Iran's representative at the UN in New York.
Conservatives in Iran have criticized Pezeshkian's choice of vice president, among other things because Zarif's children have American citizenship after being born during his time in the USA. Iran does not recognize dual citizenship.
