 Born in Muro Lucano, he was ordained to the priesthood on August 12, 1928.On January 5, 1955, Mennonna was appointed Bishop of Muro Lucano by Pope Pius XII.He received his episcopal consecration on the following March 13 from Archbishop Domenico Picchinenna, with Bishop Matteo Sperandeo and Archbishop Augusto Bertazzoni serving as co-consecrators.