The present Llantarnam Abbey - home to the Sisters of St Joseph of Annecy - is built on the site of a medieval Cistercian Monastery, founded in 1179 from Strata Florida in West Wales. Llantarnam Abbey lies about 5 miles west of Newport in South Wales. In 1538, during the Reformation, the Monastery was dissolved, suffering the fate of most monasteries throughout England and Wales.

In 1553, the property was bought by William Morgan, a Catholic, who adapted the monastic building and turned it into a family home.
In the 1830's Reginald Blewitt claimed the property and restored it. He also made some additions and re-built the Great Hall.
Later still, the property was owned by Sir Clifford Cory JP who added some features, such as a small house, known as the Monk's Cell.

During the Second World War, the property was used as a storage centre for RAF uniforms. The property came on the market in 1946 and it was bought by the Sisters of St Joseph of Annecy as a central house for the Sisters in the UK and Ireland.

Since the foundation of the Abbey in 1179, there have been Catholic links. Even after the dissolution of the Monastery, the new owner, William Morgan, was a Catholic. he faithfully paid his fines for non-attendance at the Established Church. When the Jesuit priests returned to the area in the early 17th Century, it was the Morgans of Llantarnam who helped to establish them at the Cwm, near Monmouth. St David Lewis was also a Jesuit priest, and was therefore, forbidden to say Mass or even to act as a priest. He was captured close to the Abbey opposite the present day inn, The Greenhouse. He was martyred for his faith at Usk in 1679 and canonised as a Martyr Saint in 1970.