Career
He was elected, probably by acclamation, after several days of street fighting that followed the assassination of his predecessor, Pietro Tradonico, in September 864. By the end of the year, the assassins were captured, convicted, and executed, probably beheaded. Orso instituted elected judges who would serve as magistrates as well as counsellors to the Doge.
Orso also reorganized the ecclesiastical structure of the islands of Venice by securing the creation of five new bishoprics, thus thwarting the domination of the Patriarch of Aquileia and the Patriarch of Grado.
Orso, like Tradonico, continued the fight the Slavic and Saracen pirates, which inhabited the Adriatic. He was aided by newly constructed larger ships.
Orso presented to the Byzantine emperor Basil I a bell for the basilica Hagia Sophia.
