Born in the Istrian town of Vistar (now Veštar) near Pola (Pula) in modern-day Croatia, Maximianus was consecrated bishop of Ravenna in 546 by Pope Vigilius in Patras, Greece.

To a modern art historian Meyer Shapiro, "Maximian was "a poor deacon of Pola who rose to a high position through his political adroitness" as a protégé of Justinian I.

He had not been wanted as archbishop by the people of Ravenna, but "by shrewd maneuvers he overcame their opposition, and won their respect by his discretion, generosity, and great enterprises of church building and decoration".

[1] He completed the Basilica of San Vitale and Sant'Apollinare in Classe in Ravenna, and built several other churches, including Santa Maria del Canneto in his native Istria.

Maximianus devoted himself to the revision of liturgical books and to the emendation of the Latin text of the Bible, and commissioned a large number of illuminated manuscripts.