The Basilica has a harmonious façade, enriched by a marble prothyrum, Tuscan and Ionic pilasters and a tympanum. The Church was built by the Jesuits (1608), together with the adjoining College, on the occasion of the beatification of Luigi Gonzaga, brother of Francesco who ruled Castiglione at the time. It was completed in 1610, consecrated in 1962 by Monsignor Poma, Bishop of Mantua, and erected a Basilica by Pope Paul VI on 21 June 1964. The interior recalls the structure of Vignola's Church of Jesus in Rome and was built in accordance with the canons imposed by the Council of Trent. The 17th-century design is by the Jesuit Luca Bienni of Salò. After a long interruption, work was resumed in 1761. Based on a design by Paolo Soratino of Lonato, the presbytery was rebuilt, the dome was raised and the marble complex of the new high altar with the altarpiece depicting St. Louis praying before the Virgin in the centre was placed.
The two marble statues on either side symbolise Innocence and Penance and are a clear Aloysian reference. Above it all is the Eucharistic triumph. Inserted into the structure of the altar is the urn containing the relic of St. Louis: the sacred skull which, brought from Rome in 1610, was first solemnly placed in the Palatine Church of St. Sebastian and then transferred to the Basilica named after the Saint in 1679. A precious organ, the work of Gerolamo Bonatti of Desenzano (1794), was placed in the choir loft to the right of the presbytery. The instrument retains its original features. An inscription recalls that in 1859 some pipes, kept in the small room next to the manticeria room, were removed by the Piedmontese and French soldiers who, after the victory, went around festively "ziffolando" through the streets of the village. Also in the presbytery, opposite the sacristy, in a small side chapel, the bodies of the Venerable nieces of St. Louis are displayed in three urns: Cinzia, Olimpia and Gridonia, foundresses of the 'Noble College of the Virgins of Jesus'. They were the first to follow the example of their uncle, consecrating themselves to God in a life of prayer and dedication to their neighbour, in teaching and in educational work. On the floor of the church, in a niche in front of the presbytery, a plaque recalls that Charles I, third prince of Castiglione and nephew of St Louis, is buried there. It was he who had the Saint's precious relic transported to this church (1679).