As the Vatican announced on Thursday, Francis also accepted the resignation of the previous head of the diocese, Cardinal Giuseppe Betori (77), due to his age.
The Italian has headed the archdiocese since 2008 and has also held various positions in the Italian Bishops' Conference, including Secretary General.
His successor Gambelli comes from the Tuscan coastal town of Viareggio and has been a priest in the Archdiocese of Florence since 1996.
Most recently, he headed the parish of "Madonna della Tosse" (Our Lady of the Cough).
According to popular belief, the image of the Virgin Mary there was said to have healing powers for children suffering from whooping cough, hence the name.
Gambelli previously worked as a priest
for eleven years in Chad in Central Africa, among other places.