Flavius Dalmatius, the son of Constantius Chlorus and Flavia Maximiana Theodora, and thus half-brother of the Emperor Constantine I, had spent his youth in the Gallic Tolosa.

It is probable that his two sons, Dalmatius and Hannibalianus, were born there.

During the mid-320s, Flavius Dalmatius had returned to Constantinople, to the court of his half-brother, and been appointed consul and censor in 333.

In Antioch, Flavius is responsible for the security of the eastern borders of the realm.

During this period, he examines the case of bishop Athanasius of Alexandria, the important opponent of Arianism, who is accused of murder.

In 334, Flavius had suppressed the revolt of Calocaerus, who had proclaimed himself emperor in Cyprus.

In the following year he sends some soldiers to the council of Tyros to save the life of Athanasius.