In common with many ancient European sea ports, the patron saint of the city (since the 14th century) is St Nicholas of Myra.
The Roman Catholic diocese of Galway was created in 1831 AD following the abolition by the Holy See of the Wardenship of Galway. It was united with the diocese of Kilmacduagh (est. 1152 AD) and given the administratorship of the diocese of Kilfenora (est. 1152 AD) in 1883. Its full name is the Diocese of Galway, Kilmacduagh and Apostolic Administratorship of Kilfenora.
The diocese is under the patronage Our Lady Assumed into Heaven and St Nicholas (Galway), Saint Fachanan (Kilmacduagh) and St Colman (Kilfenora). As the diocese of Kilfenora is in the Ecclesiastical Metropolitan Province of Cashel the Bishop of Galway is its Apostolic Administrator rather than its bishop. The dioceses of Galway and Kilmacduagh are in the Ecclesiastical Metropolitan Province of Tuam. The current bishop is Most Rev. Martin Drennan, installed 3 July 2005. Of the 38 parishes in the RC diocese 14 are situated in the City and are divide into two deaneries - the deanery of Galway City West and of Galway City East. In each deanery a Vicar Forane exercises limited jurisdiction on behalf of the bishop.
In the Church of Ireland, Galway is a parish of the United Diocese of Tuam, Killala and Achonry. The principal church of the parish is the St. Nicholas' Collegiate Church (founded 1320). Russian, Romanian, Coptic, and Mar Thoma Syrian Orthodox Churches use the facilities of St Nicholas Collegiate Church for their services.
The Ahmadiyya-run Galway Mosque, opened in 2014, is the only purpose-built mosque in Galway.