Although never formally canonized by the church, St. Michael enjoyed considerable popularity from the earliest days of his cult in the ancient Near East. As we have seen, at his cultic centers across Asia Minor, the archangel was invoked in accordance with his stature as a healer long before formal liturgical festivals became the normative means of expressing devotion to him. After the Eastern church began to formalize devotions to St. Michael, possibly in the late fourth or early fifth centuries (i.e., in the aftermath of the first Council of Laodicea), the archangel came to enjoy a number of different feast days in the East.

Traditionally in the West, however, St. Michael has been celebrated on two principal feast days, May 8 and September 29, both of which originated with the cult of the archangel in Italy. Though no longer celebrated in the Roman calendar, the date May 8 holds special significance for the cult of St. Michael since it allegedly marks the day of both the archangel's legendary apparition to consecrate his own church and his intercession on behalf of the Sipontans in their victory over the pagan Neapolitans. The special feast instituted to commemorate this victory spread over the entire Latin Church but was later abandoned in favor of the feast of September 29. The September date became the main feast of St. Michael, associated with the dedication of a church to the archangel on the Salarian Way, six miles north of Rome.