Sergio Franci Galli was one of three children born to a Neapolitan father and Ligurian (Genoa) mother. Sergio, Mirella, and Fausta were all born in the Lombardy District. This includes Milan, Cremona, and the smaller village of Codogno – where he was born. 

As a child, Franchi sang for the family with his father, who played the piano and guitar. At age ten, he sang a comic role as a hunchback in a school play. Young Franchi formed a three-piece band at age sixteen to earn pocket money, and then later sang with a male vocal group in local jazz clubs.