He is honoured as a Saint in the Roman Catholic and Eastern Orthodox Churches and his feast day is August 14.

Thus in April 397, the aged Simplician was elected bishop of Milan, at that time capital of the Western Roman Empire.

The most important act of his episcopate was the receipt in Milan of the relics of the three martyrs Sisinnius, Martyrius and Alexander, sent from Trento by the bishop Vigilius.

He also consecrated Gaudentius of Novara a bishop, and according to the 13th-century writer Goffredo of Bussero, he organized the texts of the Ambrosian liturgy.

[6] In 1582 St Carlo Borromeo, the cardinal archbishop of Milan, ordered a canonical recognition of Simplicianus' remains who were tumulated under the major altar[7] and then his holy relics were translated during a solemn procession to the odiern temple.