Throwing off his military belt, weapons, and vine staff (the symbol of his rank),[2] Marcellus was soon brought before a judge named Fortunatus.

Afterwards, it is said that the official shorthand writer, a man named Saint Cassian, was so angry at the sentence that he refused to record the court proceedings and was martyred as well.

An alternative version of his legend states that he was a centurion of the Legio VII Gemina Pia Felix, and was born in what is now León, Spain, in the middle of the third century.

During the birthday celebrations for the Emperor Maximian, in July 298, Marcellus publicly demonstrated his Christian faith by throwing down the insignia of his rank, and proclaimed that he venerated only one God.

He was condemned to death and decapitated on October 29, 298, together with his wife Nona and his twelve sons (Claudius, Lupercus, Victorius, Facundus, Primitivus, Servandus, Germanus, Faustus, Januarius, and Martial).

Their relationship to Marcellus is probably apocryphal, though it was accepted in subsequent breviaries and hagiographies as well as the Roman Martyrology, which placed all four saints under October 30.