Upon the defeat of Melus, who had rebelled against the Byzantines, at the battle of Cannae in 1018, Argyrus and his mother were captured and taken to Constantinople as prisoners.
In 1040, the Lombards of southern Italy revolted against their Greek overlords, with the support of Norman mercenaries, and slew the catepan Nikephoros Dokeianos.
In February 1042, the original nominal leader, Atenulf, brother of the prince of Benevento, defected with the catepan's ransom money to the Greeks and was replaced by Argyrus.
It is assumed that he received a bribe of money from Constantine IX, who certainly wrote him letters offering it, and the title of catepan of Italy.
When the revolt in Apulia was suppressed, the Byzantines, under advice from Argyrus, who travelled to Constantinople and received the title of "Duke of Italy, Calabria, Sicily, and Paphlagonia", formed an alliance with the Papacy to counter the emergence of the Norman menace in the area.