The Diocese of Calbayog is the local church comprising the civil territorial jurisdiction of western Samar Island. The island, the third largest in the Philippines, is composed of three provinces: Northern Samar with Catarman as capital, Eastern Samar with Borongan as capital and the Samar Province with Catbalogan as the capital. The City of Calbayog is where the Cathedral of the diocese is located since its ecclesiastical foundation on April 10, 1910, by Pope Pius X. The new Diocese was before made of the whole Samar and Leyte islands.
On April 28, 1934, Pope Pius XI promulgated an apostolic constitution with the incipit Romanorum Pontificum semper separating the dioceses of Cebu, Calbayog, Jaro, Bacolod, Zamboanga and Cagayan de Oro from the ecclesiastical province of Manila. The same constitution elevated the diocese of Cebu into an archdiocese while placing all the newly separated dioceses under a new ecclesiastical province with Cebu as the new metropolitan see.[2]
Subsequently, Palo was ceded from Calbayog as a separate diocese in 1937, Borongan in 1965 and Catarman in 1975.
The historical vicissitudes of the Diocese of Calbayog cannot be fully appreciated apart from the history of the early evangelical works of the first missionaries who came to Samar. The first Jesuit missionaries reached Leyte and Samar in 1595, the islands subsequently forming part of the Diocese of Cebu until erected into a separate diocese on 10 April 1910. The first bishop was Pablo Singzon de la Anunciacion.
^Pope Pius XI, Apostolic Constitution separating some dioceses from the ecclesiastical province of Manila to form the new ecclesiastical province of CebuRomanorum Pontificum semper (28 April 1934), Acta Apostolicae Sedis 27 (1935), pp.263-264. PROVINCIA ECCLESIASTICA MANILANA DISMEMBRATIO ET NOVA CAEBUANA PROVINCIA ERIGITUR.