Dalmatius was the nephew of Constantine I. His father was the half-brother of Constantine and served as censor. Dalmatius and his brother Hannibalianus were educated by rhetor Exuperius. On 18 September 335 CE, he was raised to the rank of Caesar. Dalmatius died in late summer 337 CE, killed by his own soldiers. It is possible that his death was related to the purge that hit the imperial family at the death of Constantine, and organized by Constantius II with the aim of removing any possible claimant to imperial power other than the sons of the late emperor.