He was born in Antioch, (in modern-day Turkey but historically in Syria), to a prominent and wealthy family.

Saint Domnius was martyred with seven other Christians in the persecutions of the Emperor Diocletian, and was buried in the Manastirine cemetery, outside the walls of Salona.

[4] When Salona was sacked by the Avars and Slavs in the 6th century, the population eventually moved to the nearby Palace of Diocletian, enlarging the nearby city of Split (Spalatum), and establishing it as the successor to Salona.

[6] Part of the celebration includes a procession led with a silver reliquary of the saint's relics.

[5] The Basilica of St. John Lateran in Rome claims to own some of Domnio's relics, since Pope John IV, in the 7th century, had requested that relics of a martyr named Domnio be brought to Rome.