The priory's beginnings were tangled in ecclesiastical real estate. Documents preserved at Gloucester Cathedral record that Chertsey Abbey in Surrey had misappropriated the Cardigan church and was eventually forced to yield it up. Gloucester Abbey had been the rightful holder by Gilbert de Clare's grant. The Brut y Tywysogion — the great medieval Welsh chronicle of princes — confirms that de Clare made the grant before his death in or around 1117. Then in 1164 the calculus changed entirely: Rhys ap Gruffydd, the Lord Rhys, prince of South Wales, recaptured Cardigan from the Normans and made the place Welsh again. Rhys confirmed the priory's existence by grant but redirected it to the Benedictines of Chertsey Abbey, and changed its dedication from the Trinity to St Mary.

The priory occupied 200 acres on the south bank of the River Teifi, sharing a boundary with Cardigan Castle itself — a strategic and a holy site adjoining, as so often in medieval Wales. The grounds and buildings stretched along the riverbank, with orchards, mills, fishponds and a chantry chapel that probably housed the tomb of Sir John ap Jevan. When the Bishops of St Davids came to Cardigan, they stayed at the priory. In 1433 or 1434 the abbot of Chertsey noted certain problems at the place, never spelled out in the surviving record, but suggesting that the Bishops' presence may not always have been welcome. A 1599 map shows the church as a simple cruciform; Joan Blaeu's 1646 map adds a chapel jutting from the cross.

Henry VIII's Dissolution of the Monasteries ended Cardigan Priory's religious life in 1538 or 1539. The buildings passed to lay hands — first to Bisham in Berkshire, then to William and Mary Cavendish in 1539 or 1540 — and the religious community dispersed. But a hundred years later the priory's afterlife produced its most famous resident. Katherine Philips, born in London in 1632, married into the Philipps family of Cardiganshire and made Cardigan Priory her favoured Welsh home. She wrote poetry under the name Orinda — "The Matchless Orinda" to her admirers — and built a literary salon by correspondence with the leading writers of the Restoration. Her translations of Corneille were staged in Dublin in 1663 to acclaim. She died of smallpox in 1664, aged only thirty-two, just as her career was opening. She did some of her best work at Cardigan.

The priory itself, as a building, is gone. What remains is the church — St Mary's, Cardigan, still serving as the parish church on the priory's former site, Grade II* listed, a survivor where the cloisters and refectory long since became masonry for later buildings. The footprint of the priory grounds runs through modern Cardigan as a green spine along the river, with the castle at its head and what was once the river-side priory at its foot. The 200 acres are mostly absorbed into housing and gardens now. But the relationship between site and water still tells the medieval story: the Teifi was the priory's road to Bristol, to Ireland, to the wider world, and the Benedictines knew where to build.

Stand outside St Mary's Church on a grey Welsh afternoon, and the layers come into view. A Norman knight gave land here. A Welsh prince reclaimed it. Benedictine monks farmed it for four centuries. A king's commissioners dismantled it. A 17th-century woman wrote some of the finest love poems in English in rooms on this ground. The place keeps doing what places do: collecting people, holding them for a while, then letting them go and waiting for the next.