There was a church on the site of St Mary's since circa 1328, erected by Henry de Gower, Bishop of Saint David's. One Sunday morning, in 1739, the roof of the nave collapsed into the church while the congregation was waiting to enter the building. The whole structure was re-built apart from the tower. 1822 saw the church being lit by gas for the first time with thirty six lamps. The church underwent complete renovation between 1879 and 1882 by Vicar Dr Morgan. In 1896, the church was flattened and rebuilt again under the designs of Arthur Blomfield by Dean Allan Smith, though some parts of the old church survived the re-development. In February 1941 the church was extensively damaged by Bombing during the Blitz. It was not rebuilt until the 1950s.
From the 1890s the Swansea Devil stood on a set of buildings facing the west side of the church, constructed by a disgruntled rival of Blomfield's, angry at the commissioning of Blomfield's designs over his own.
References:The Church of St Donatus name refers to Donatus of Zadar, who began construction on this church in the 9th century and ended it on the northeastern part of the Roman forum. It is the largest Pre-Romanesque building in Croatia.
The beginning of the building of the church was placed to the second half of the 8th century, and it is supposed to have been completed in the 9th century. The Zadar bishop and diplomat Donat (8th and 9th centuries) is credited with the building of the church. He led the representations of the Dalmatian cities to Constantinople and Charles the Great, which is why this church bears slight resemblance to Charlemagne's court chapels, especially the one in Aachen, and also to the Basilica of San Vitale in Ravenna. It belongs to the Pre-Romanesque architectural period.
The circular church, formerly domed, is 27 m high and is characterised by simplicity and technical primitivism.