Feast day
The feast day of Saint Gabriel the Archangel was exclusively celebrated on 18 March according to many sources dating between 1588 and 1921; unusually, a source published in 1856 has the feast celebrated on 7 April for unknown reasons (a parenthetical note states that the day is normally celebrated on 18 March). Writer Elizabeth Drayson mentions the feast being celebrated on 18 March 1588 in her 2013 book "The Lead Books of Granada".
One of the oldest out-of-print sources placing the feast on 18 March, first published in 1608, is Flos sanctorum: historia general de la vida y hechos de Jesu-Christo ... y de los santos de que reza y haze fiesta la Iglesia Catholica ... by the Spanish writer Alonso de Villegas; a newer edition of this book was published in 1794. Another source published in Ireland in 1886 the Irish Ecclesiastical Record also mentions 18 March.
The Feast of Saint Gabriel was included by Pope Benedict XV in the General Roman Calendar in 1921, for celebration on 24 March. In 1969, the day was officially transferred to 29 September for celebration in conjunction with the feast of the archangels Ss. Michael and Raphael. Today, the 29 September date (known as Michaelmas) has been adopted by not only the Catholic Church, but also the Church of England, the Lutheran churches, the Anglican Communion, and the Western Orthodox churches.
The Eastern Orthodox Church and those Eastern Catholic Churches that follow the Byzantine Rite celebrate the Feast of the Archangels (Synaxis of the Archangel Michael and the Other Bodiless Powers) on 8 November. For those churches that follow the traditional Julian Calendar, 8 November currently falls on 21 November of the modern Gregorian Calendar, a difference of 13 days. Eastern Orthodox commemorate Gabriel not only at the Feast of the Archangels, but also on two other days:
26 March, the "Synaxis of the Archangel Gabriel" and celebrates his role in the Annunciation
13 July, also known as the "Synaxis of the Archangel Gabriel", which celebrates all the appearances and miracles attributed to Gabriel throughout history. The feast was first established on Mount Athos when, in the 9th century, during the reign of Emperor Basil II and Empress Constantina Porphyrogenitus and while Nicholas Chrysoverges was Patriarch of Constantinople, Gabriel appeared in a cell near Karyes, where he wrote with his finger on a stone tablet the hymn to the Theotokos, "It is truly meet ...".
Saint Gabriel the Archangel is commemorated on the vigil of the Feast of the Annunciation by Antiochian Western Rite Vicariate and Western Rite in the ROCOR.
The Coptic Orthodox Church celebrates Gabriel's feast on 13 Paoni, 22 Koiak, and 26 Paoni. One medieval Coptic work, the Investiture of the Archangel Gabriel, attributes the feast day of 22 Koiak to the day Gabriel was given the rank of archangel in heaven.
The Ethiopian Church celebrates Gabriel's feast on 18 December (in the Ethiopian calendar), with a sizeable number of its believers making a pilgrimage to a church dedicated to "Saint Gabriel" in Kulubi and Wonkshet on that day.