Fiordelli was born in Città di Castello on 1916, he had a brother named Furio and three sisters, Gina, Maria and Dina.

Ordained priest on November 6, 1938 and graduated at Pontifical Lateran University.

Fiordelli held the office of bishop for 37 years, welcoming pope John Paul II on March 19, 1986 on a visit to Prato.

Monsignor Fiordelli was known in 1958 for having defined the Bellandi family (Mauro Bellandi and Loriana Nunziati) public sinners, a couple of citizens of Prato who had married in a civil ceremony.

Fiordelli was tried for defamation: he was sentenced in the first instance to pay a fine of 40.000 liras, and acquitted on appeal for the "unquestionable act".