Marchal is due to arrive in France around midday on Saturday, a French presidency official said.
French President Emmanuel Macron urged Iran to also release Fariba Adelkhah, who is still imprisoned, the official added. Adelkhah also holds French and Iranian passports.
Iran and France agreed to swap Marchal, held on security charges, and an Iranian detained by Paris over alleged violations of US sanctions against Tehran, Iranian state media reported on Friday.
France has released Jalal Ruhollahnejad, an Iranian engineer wanted by US authorities over sanctions charges, state broadcaster IRIB has reported.
France had demanded that Iran release Marchal, a senior researcher at Sciences Po university whose arrest was reported by Paris in mid-October.
In May, a French court approved the extradition of Rouhollahnejad to the United States to face charges of attempting to illegally import US technology for military purposes on behalf of an Iranian company which US officials said was linked to the elite Revolutionary Guards.
The detentions have coincided with a protracted standoff with Western powers prompted by a US decision to withdraw from an international agreement to curb Iranian nuclear activities.
Their Paris-based support group and the French foreign ministry have sounded the alarm over the health of both detainees -- Adelkhah went on hunger strike for 49 days and Marchal's health was said to be deteriorating.
The support group has repeatedly claimed that the two are innocent of the charges they face.
Adding to concerns for the welfare of the prisoners, Iran has been hard hit by the novel coronavirus pandemic, behind only Italy and China in number of fatalities.
Iran this week temporarily released 85,000 prisoners with 10,000 more slated to receive pardons, as fears mount the new coronavirus could sweep through the country's overcrowded prisons.
British-Australian academic Kylie Moore-Gilbert, who was being held alongside Adelkah, was not been listed among those to be freed.
British-Iranian aid worker Nazanin Zaghari-Ratcliffe, held since was among those who received furlough.
(with agencies)
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