This Romanesque - Gothic building was built during the 13th and 14th centuries. However, beyond the walls little survived the test of time. Various rebuildings were carried out with the first major restoration undertaken in 17th century determining the present structure. At the end of that century, the bishop of Guarda, Martins de Melo, began rebuilding but it was when Castelo Branco was elevated to the status of bishopdom in 1771 that the greatest amount of work was done. It served as the cathedral through to 1881 when it was annexed onto the bishopdom of Portalegre.
On the spacious interior, there are the 17th century altarpieces with canvas paintings by Bento Coelho da Silveira and the alterations carried out early in the 19th century on the orders of bishop Vicente Ferrer da Rocha. He was responsible for installing the organ in the main chapel and building the Chapel of Santíssimo Sacramento, with its Pedro Alexandrino paintings, and the sacristy. In both, there is an exuberant style that effectively combines Baroque, Rocaille and Neo-classical influences.