The earliest evidence of Christian presence in the area is a tombstone, which Edmond-Frédéric Le Blant dated to the fourth century.

[1] When the Concordat of 1802 reestablished this diocese, it accorded to it also the département of Tarn, which was detached from it in 1822 by the creation of the Archdiocese of Albi; and from 1802 to 1822, Montpellier was a suffragan of Toulouse.

Local traditions, recorded in 1583 by Abbé Gariel in his Histoire des évêques de Maguelonne, affirm that St. Simon the Leper, having landed at the mouth of the Rhône with St. Lazarus and his sisters, was the earliest apostle of Maguelone.

Urban II charged the Bishop of Maguelone to exercise the papal suzerainty, and he spent five days in this town when he came to France to preach the First Crusade.

Pope Clement IV reproached (1266) Bishop Bérenger Frédol with causing to be struck in his diocese a coin called "Miliarensis", on which was rend the name of Mahomet; in fact at that date the bishop, as well as the King of Aragon and the Count of Toulouse, authorized the coinage of Arabic money, not intended for circulation in Maguelone, but to be sold for exportation to the merchants of the Mediterranean.

James III of Majorca sold Montpellier to Philip VI (1349); and the city, save for the period from 1365 to 1382, was henceforth French.

At the request of King Francis I, who pleaded the epidemics and the ravages of the pirates which constantly threatened Maguelone, Pope Paul III transferred the see to Montpellier (27 March 1536).

Among the 54 bishops of Maguelone, and the 18 bishops of Montpellier, may be mentioned: Blessed Louis Aleman (1418–1423), later Bishop of Arles; Guillaume Pellicier (1527–68), whom king Francis I of France sent as an ambassador to Venice, and whose leaning as a humanist and naturalist made him after Scévole de Sainte-Marthe "the most learned man of his century"; the preacher Pierre Fenouillet (1608–52); François de Bosquet (1657–76), whose historical labours were very useful to the celebrated Baluze; the bibliophile Colbert de Croissy (1696–1738), who induced the Oratorian Pouget to compose in 1702 the famous "Catechism of Montpellier", condemned by the Holy See in 1712 and 1721 for Jansenistic tendencies; Fournier (1806–34), who in 1801 was confined for a time in the madhouse at Bicêtre at the command of Napoleon I Bonaparte, for a sermon against the Revolution.

Tiberius and Modestus and St. Florence, martyrs at Agde under Diocletian; St. Severus, Abbot of St. André, at Agde (d. about 500); Saint Maxentius, a native of Agde and founder of the Abbey of St-Maixent, in Poitou (447–515); St. Benedict of Aniane, and his disciple and first historian, Saint Ardo Smaragdus (d. in 843); St. Guillem, Duke of Aquitaine, who in 804, founded near Lodève, on the advice of St. Benedict of Aniane, the monastery of Gellone (later St-Guillem du Désert), died there in 812, and under the name of "Guillaume au Court Nez" became the hero of a celebrated epic chanson; St. Etienne, Bishop of Apt (975–1046), born at Agde; Blessed Guillaume VI, Lord of Montpellier from 1121 to 1149 and who died a Cistercian at Grandselve Abbey; Peter of Castelnau, Archdeacon of Maguelone, inquisitor (d. in 1208); Gérard de Lunel (St. Gerard), Lord of Lunel (end of thirteenth century); the celebrated pilgrim, St. Roch, who was born at Montpellier about the end of the thirteenth century, saved several cities of Italy from the pest, and returned to Montpellier to live as a hermit, where he died in 1325.