It is believed, also in consideration of the title of "plébain" traditionally attributed to the parish priest, that the parish of Morgex is among the oldest in the upper Valle d'Aosta. This hypothesis has been confirmed by archaeological investigations which have brought to light the remains of the ancient early Christian baptismal church (5th-6th century), while the church of Morgex is mentioned for the first time in the bull of Pope Alexander III of 1176.
The medieval church was remodeled several times, until it received its current layout with the restoration and expansion campaign that began in 1687, at the end of which, in 1705, Mons. d'Arvillars consecrated the building.
The internal decoration is the result of interventions by the Savoyard painter Girollet as regards the vaults of the apse area (18th century), while the rest is the work of the painter Lancia, active in the first half of the 20th century.
Of the ancient decoration of the church, a Last Supper on the left side of the central nave, dated 1559, and the interesting frescoes of the fifteenth-century chapel at the end of the left nave remain. Noteworthy is the main altar, very rich in friezes and gilding, dating back to the beginning of the eighteenth century, even if the central painting depicting the Assumption of Mary was replaced with a painting by Lancia after a fire in 1931 had destroyed that original.
Of particular historical and artistic value is the wooden crucifix dating back to the end of the fourteenth century which dominates the central nave.
The bell tower is divided into six superimposed registers marked by hanging arches. The domed cusp rests on an octagonal lantern and is covered in copper and surmounted by a wrought iron cross with a rooster