Euphemius is an imperial admiral, probably born in Messina.

In about 826, according to Michele Amari, the Emperor had appointed a new governor of Sicily called either Constantine or Photinus, who in turn had entrusted a naval command to Euphemius, a landowner with a large following; accused on a perhaps trumped-up charge of abducting a young nun from a convent, he organized an uprising against the Emperor, Michael II and, after some military successes, proclaims himself emperor in Syracuse, independent from Constantinople.

In practice, he is a charismatic chief, and, respected as a king, the title of emperor means that he dominates the whole territory of the island.

Realizing that he would be defeated by imperial troops when reinforcements are sent from the East, he appeals to the Muslim leaders of Ifriqiya, where he asks the help of Arabs to take Sicily and Malta from the Empire.

Joining his forces with a large fleet commanded by the jurist Asad ibn al-Furat in the high summer of 827, he dies later this year, killed by members of the imperial garrison at Castrogiovanni, modern day Enna.

He is considered to be the man who initiated the Arab invasion of Sicily and Malta and the beginning of the two-century Islamic domination on the island as the Emirate of Sicily.