St David's Cathedral (Welsh: Eglwys Gadeiriol Tyddewi) is situated in St David's, Britain's smallest city, in the county of Pembrokeshire, near the most westerly point of Wales.

The monastic community was founded by Saint David, Abbot of Menevia, who died in 589. Between 645 and 1097, the community was attacked many times by raiders, including the Vikings; however it was of such note as both a religious and an intellectual centre that King Alfred summoned help from the monastic community at St David's in rebuilding the intellectual life of the Kingdom of Wessex. Many of the bishops were murdered by raiders and marauders, including Bishop Moregenau in 999 and Bishop Abraham in 1080. The stone that marked his grave, known as the "Abraham Stone", is intricately carved with early Celtic symbols and is now on permanent display within the Cathedral Exhibition at Porth-y-Tŵr.

In 1081, William the Conqueror visited St David's to pray, and thus recognised it as a holy and respected place. In 1089, the shrine of David was vandalised and stripped of its precious metals. In 1090, the Welsh scholar Rhigyfarch wrote his Latin Life of David, highlighting David's sanctity, thus beginning the almost cult-like status he achieved.

In 1115, with the area under Norman control, King Henry I of England appointed Bishop Bernard as Bishop of St David's. He began to improve life within the community, and commenced construction of a new cathedral. In 1123, Pope Calixtus II granted Bishop Bernard's request to bestow a papal privilege upon St David's, making it a centre of pilgrimage for the Western world; the Pope decreed that "Two pilgrimages to St David's is equal to one to Rome, and three pilgrimages to one to Jerusalem". The new cathedral was quickly constructed and Bishop Bernard consecrated it in 1131. Henry II of England's visit in 1171 saw the following of David increase and the need for a larger cathedral. The present cathedral was begun in 1181 and completed not long after. Problems beset the new building and the community in its infancy: the collapse of the new tower in 1220 and earthquake damage in 1247/48.

Under Bishop Gower (1328–1347) the cathedral was modified further, with the rood screen and the Bishops Palace intended as permanent reminders of his episcopacy; the palace is now a picturesque ruin. In 1365, Bishop Adam Houghton and John of Gaunt began to build St Mary's College and a chantry. He later added the cloister, which connects it to the cathedral. The episcopacy of Edward Vaughan (1509–1522) saw the building of the Holy Trinity chapel, with its fan vaulting which some say inspired the roof of King's College, Cambridge. This period also saw great developments for the nave, whose roof and Irish oak ceiling were constructed between 1530 and 1540. Bishop Barlow, unlike his predecessor as bishop, wished to suppress the following of David, and stripped St David's shrine of its jewels and confiscated the relics of St David and St Justinian in order to counteract "superstition" in 1538. In 1540, the body of Edmund Tudor, Earl of Richmond and father of Henry VII, was brought to be entombed in front of the high altar from the dissolved Greyfriars' Priory in Carmarthen.

The establishment of the Commonwealth of England under Oliver Cromwell greatly affected many cathedrals and churches, and was particularly felt in St David's. The cathedral was all but destroyed by Cromwell's forces and the lead was stripped from the Bishops Palace roof. There is a pronounced slope to the floor of the cathedral, amounting to a height difference of nearly four metres between the east and west ends, and the building is still shifting minutely.

The Welsh architect John Nash was commissioned to restore the west front in 1793 to repair the damage done two hundred years previously. Eclectic in style (with Gothic and Perpendicular characteristics – the latter attributed partly to his destruction of the windows of the chapel of St Mary's College in order to reuse that tracery for his west front), his work soon proved to be substandard (as had his previous work on the chapter house). Within a century the Nash west front had become unstable and the whole building was restored by George Gilbert Scott between 1862 and 1870. The lady chapel was restored by public subscription in 1901 and the eastern chapels were restored through a legacy of the Countess of Maidstone, granddaughter of Bishop John Jenkinson, between 1901 and 1910.

The cathedral suffered the pains of disestablishment in 1923, as did the whole Church in Wales. The diocese was made smaller by the removal of the Archdeaconry of Brecon to form the new Diocese of Swansea and Brecon. However, this left a large area as a diocese to govern and St David's began to deteriorate as the centre of the diocese, being nowhere near the centre – the bishop's residence had been at Carmarthen since the 16th century, but administration and the focus moved from the cathedral to the diocese's now largest town.

The 1950s saw the appointment of the Reverend Carl Witton-Davies as Dean; appointed in his thirties, his driving vision and energy was short-lived as he was offered what some was believed as a preferment as Archdeacon of Oxford, but did not leave that position for the rest of his service in the church. The cathedral began to have life again and the famous Welsh Youth Pilgrimages to St David's (Cymry'r Groes) led many to a life of service in the church and provided the Church in Wales with inspired clergy for a decade following. It was Grade I-listed by Cadw in 1951.

The 1960s saw the restoration of St Mary's College as the cathedral hall, for the use of the cathedral parish and for use as an area for art exhibitions and poetry readings. It was dedicated by Archbishop Edwin Morris in 1966 and the inaugural event was a poetry reading by the poet R. S. Thomas, who served as a vicar in the Bangor diocese.

During the 1980s a number of official events in cathedral life took place: in 1981, Charles, Prince of Wales, visited to celebrate the 800th anniversary of the consecration of the cathedral; and on Maundy Thursday 1982, Queen Elizabeth II distributed the Royal Maundy at the cathedral. This was the first occasion that the ceremony had taken place outside England. In 1989–90, the 1,400th anniversary of the death of St David was presided over by the Archbishop of Wales, George Noakes, who was also diocesan Bishop of St David's.

The decades leading to and immediately following the year 2000 have been the most notable in the cathedral's history since its construction.^{[citation needed]} First, the British Government decided to reinstate the title of "city" to St David's and this was formally conferred by Queen Elizabeth II on 1 June 1995. The task that lay before the dean, the Very Reverend Wyn Evans, on his appointment in 1994 was huge: a new organ was badly needed and the west front needed extensive restoration. It was also thought to be time for the cathedral to invest in its future by creating a visitor centre within the bell tower, enlarging the peal of bells from eight to ten and by the "reconstruction", or completion, of the cathedral cloisters to house the cathedral choir, vestries, an education suite, rooms for parish use and a refectory as a reminder of the monastic beginnings. The first project was the restoration of the west front, with the original quarry that was used for stone at Caerbwdi Bay being reopened. This phase was completed in 1998, in time for the organ to be dismantled and rebuilt by the organ builders Harrison and Harrison of Durham. The organ was completed in the middle months of 2000 and dedicated on 15 October that year.

The ring of bells was cast by Whitechapel Bell Foundry of London and presented as a gift by the American Friends of St David's Cathedral. The substantial task of rebuilding the cloisters as an education centre and refectory began in 2003 and was completed in May 2007. The translation of Wyn Evans from dean to bishop led to the appointment of Jonathan Lean as dean in 2009.

The bells are not hung in the central tower of the cathedral but in the old gatehouse, Porth y Twr. There are 10 bells, with the heaviest weighing 24 long cwt 3 qr 25 lb (2,797 lb or 1,269 kg) in D. The back eight bells were cast in 1928 by Mears & Stainbank, London and two trebles added in 2000 cast by Whitechapel Bell Foundry, London.