His father died when Mario was a child, and his uncle was Giovanni Nasalli Rocca di Corneliano, who was later Archbishop of Bologna.

Upon the death of John XXIII on 3 June 1963, Nasalli Rocca and all major Vatican officials, in accord with custom, automatically lost their positions during the sede vacante.

He received his episcopal consecration on the following 20 April from Cardinal Paolo Marella, with Archbishop Diego Venini and Bishop Alberto Scola, serving as co-consecrators, in St. Peter's Basilica.

After ten years' standing as a Cardinal-Deacon, Nasalli Rocca opted to become a cardinal priest, with the same titular church, on 30 June 1979.

Cardinal Nasalli Rocca di Corneliano died in a Roman clinic, where he had been admitted a week earlier,[1] at age 85.