Baptised the day after his birth, on 13 May, he was the youngest of his parents' five surviving children, and his uncle Guido was a revered Franciscan friar.

He received the clerical tonsure on 23 December 1939, and was eventually ordained a priest on 31 October 1943 by Bishop Giuseppe Debernardi.

Benelli received his episcopal consecration on the following 11 September from Cardinal Secretary of State Amleto Giovanni Cicognani, with Archbishop Pietro Sigismondi and Bishop Mario Longo Dorni serving as co-consecrators.

These assignments gave him a deep interest in the battle against illiteracy and the Church's work for peace and economic development.

During the August conclave, Benelli supported Albino Luciani, the eventual winner, who became Pope John Paul I.

His funeral Mass was celebrated by Cicognani's successor, Agostino Casaroli, and his remains were buried in Santa Maria del Fiore cathedral.