Brecon Cathedral, (Welsh: Eglwys Gadeiriol Aberhonddu) in the town of Brecon, Powys, is the cathedral of the Diocese of Swansea and Brecon in the Church in Wales and seat of the Bishop of Swansea and Brecon. Previously the church of Brecon Priory and then the Parish Church of St John the Evangelist, it became Brecon Cathedral following the disestablishment of the Church in Wales in 1920 and the creation of the diocese in 1923.
Because of the characteristic round shape of its churchyard, the cathedral is thought to be on the site of an earlier Celtic church, of which no trace remains. A new church, dedicated to St. John, was built on the orders of Bernard de Neufmarché, the Norman knight who conquered the kingdom of Brycheiniog in 1093. He gave the church to one of his followers, Roger, a monk from Battle Abbey, who founded a priory on the site as a daughter house of Battle. The first prior at Brecon was Walter, another monk from Battle. Bernard de Neufmarché also endowed the priory with lands, rights and tithes from the surrounding area, and, after his death, it passed to the Earls of Hereford, so giving it greater prosperity. The church was rebuilt and extended in the Gothic style in about 1215, during the reign of King John. In the Middle Ages, the church was known as the church of Holy Rood or Holy Cross, because it owned a great "golden rood" which was an object of pilgrimage and veneration until it was destroyed in the Dissolution of the Monasteries in the 16th century. The smoke-blackened roof of its hall was built between 1237 and 1267.