Apart from the church, none of the abbey buildings remain. The current church is located on the site of a previous basilica of the 4th century which contained the body of Saint Saturnin or Sernin, the first bishop of Toulouse in c. 250.

Constructed in the Romanesque style between about 1080 and 1120, with construction continuing thereafter, Saint-Sernin is the largest remaining Romanesque building in Europe.

The church is particularly noted for the quality and quantity of its Romanesque sculpture. In 1998 the basilica was added to the UNESCO World Heritage Sites under the description: World Heritage Sites of the Routes of Santiago de Compostela in France.

Despite being called a basilica, Saint-Sernin’s deviates from the basilica plan of early Christian architecture in a few ways. It is much larger compared to earlier churches, measuring 104m in length.

It is also constructed mostly of brick. The building is in the form of a crucifix. The ceilings are vaulted, unlike many of the earlier churches. Saint-Sernin’s contains radiating chapels which were used to display important relics.

Another deviation from the earlier Christian churches is the addition of an ambulatory, a walkway that goes around the nave and side aisles to allow for viewing of the radiating chapels (which could be done while mass was being held without interrupting the ceremony). For these and other reasons, Saint-Sernin’s is often said to follow the “pilgrimage plan” instead of the traditional basilica plan.