Born in Pontremoli, Chiarlo studied at the seminary in Lucca and the Pontifical University of St. Thomas Aquinas (Angelicum) in Rome before being ordained to the priesthood on 28 May 1904.

[2] He received his episcopal consecration on the following 12 November from Cardinal Pietro Gasparri, with Archbishop Giovanni Volpi and Bishop Theodor Kubina serving as co-consecrators, in the chapel of the Collegio Pio-Latinoamericano in Rome.

[3] His role was then modified on 30 September 1933 with the erection of nunciatures, leaving him Apostolic Nuncio to Costa Rica, Nicaragua, and Panama, with his role as Nuncio to El Salvador and Honduras and Delegate to Guatemala assigned to Albert Levame later that year.

[3][4] Returning to Rome, he was charged with the special mission of assisting prisoners of World War II on 3 December 1941.

[6] He was replaced in Brazil by Armando Lombardi on 22 September 1954[7] and remained a nuncio at the disposition of the Secretariat of State.