The abbey church was built around 815 on the land of an ancient estate called Déas (now Saint-Philbert-de-Grand-Lieu), given to the monk Saint Philibert in the 6th century.

[3] Under the leadership of Abbot Hilbod, the site was refitted to provide a more effective defense against looters.

[5] The monks rebuilt the abbey church, then moved to Tournus in Burgundy with the relics, leaving the shrine empty.

[7][8] After the construction of the new parish church in 1869, the building was used as a market hall, and the cracked walls had to be reduced in height by 3 meters.

[12] In addition to tours of the building and gardens, art and cultural exhibitions are held in the abbey church.

The appearance of the building has also been changed, both inside and out.The current nave was rebuilt after 847, the first church dating from 815 was ruined by the Normans.

[15] Reinforced between the 9th[14] and 11th centuries (the dating of this work has given rise to controversy, due to the scarcity of available documents[16]) by Romanesque arches, the walls were however levelled for safety reasons when the building was used as a chicken market.

Originally, it consisted of three apsidioles, which were replaced after their destruction by a straight wall at chevet level.

This was the site of the fenestella, the only opening, intended to be small so that it could be easily closed in the event of danger, and which enabled pilgrims to see and touch the relics.

Crafted towards the end of the 6th century, it is made from a single block of blue granite cut in the Pyrenean quarries of Saint-Béat.

[17] The saint, buried in 686 at Noirmoutier, was exhumed in 836 and transported in four days on a stretcher on men's backs to Déas.

[15] Guillaume Chupin's tombstone dates back to 1440, when this priest had a stone engraved under which he hoped to be buried.

They were made when the abbey church was restored to worship in 1936, and are the work of master glassworker Jacques Grüber.

The window above the high altar depicts Saint Philibert with his right hand raised in a gesture of blessing, and the boat carrying his sarcophagus from the Noirmoutier monastery.

In the lower part of the window, two monks support the shrine, while a third, hands clasped, turns his head towards the audience, as if to encourage prayer.

In the ambulatory there is a second-stained glass window, a representation of Saint Anne, whose cult the Philibertine monks imported to the region from Ireland.

It reads "Aux ides de juin, dédicace au Dieu sauveur."

[15] The baptismal fonts are proof of the abbey's function as a parish church after the return of the monks in the 11th century.

[15] Lastly, the washbasin was originally intended for pilgrims to purify themselves before visiting the relics of Saint Philibert, In accordance with a medieval custom.

The unusually high position of the washbasin dates back to the 1900 excavations, when the ground level was lowered by one metre.

During the French Revolution, the priory building was sold as national property on November 8, 1791, for the sum of 10,000 francs,[15] in accordance with the Décret des biens du clergé mis à la disposition de la Nation of November 2, 1789.

[7] A former outbuilding of the abbey church with schist walls, dating from the 15th to 16th centuries, houses a bird and mineralogical museum.