He entered the Order of Friars Minor in the Roman province, receiving the habit at Cori, 1 February 1838.
For some years he taught at Tivoli, Ferentino, Viterbo, Aracoeli in Rome; in 1854 he retired to Recco in his native province of Genoa.
By order of Bernardino Trionfetti, minister-general of the Friars-Minor, Marcellino in 1856 was entrusted with the major task of writing the history of the Franciscan missions, to which the greater part of his life was devoted.
He undertook journeys all over Europe, bringing home literary treasures, especially from the libraries and archives of Spain.
During his long literary career Marcellino made the acquaintance of many prominent men, with whom he carried on a large correspondence, preserved in the convent of Livorno.