Although his father was from an equestrian family, Macrianus Minor's mother was of noble birth and her name, possibly, was Iunia. According to the often unreliable Historia Augusta, he had served as military tribune under Valerian.
Macrianus, his father and his brother Quietus, were in Mesopotamia in 260, for the Sassanid campaign of Emperor Valerian, when the Roman army was defeated, and the emperor was captured. With help from his father, who kept the imperial treasure, and by the influence of Balista, Valerian's praefect, Macrianus gained the imperial office together with his brother Quietus, through the election by the army, in contrast with the lawful Emperor Gallienus, son and co-emperor with Valerian, who was far in the West. The two emperors and brothers were recognized in the eastern part of the Empire, having a stronghold in Egypt, the grain supplying province for the city of Rome.
After having temporarily secured the Persian frontier, Macrianus Major and Macrianus Minor moved to the West to attack and eliminate their rival Gallienus.They were however defeated in autumn 261 by Aureolus, and later killed by their own soldiers at the father's request.
