Louis-François Duplessis de Mornay was born to a family of high nobility[1] on September 20, 1663, at Vannes in Bretagne.

The district north of the Ohio was entrusted to the Society of Jesus and the Priests of the Foreign Missions of Paris and Quebec; that between the Mississippi and the Rio Perdito, to the Discalced Carmelite Fathers with headquarters at Mobile.

When the Company of the West applied to him for priests for the lower Mississippi Valley he offered the more populous field of colonists to the Capuchin Fathers of the province of Champaigne, who, however, did not take any immediate steps, and it was not until 1720 that any of the order came to Louisiana.

In 1721 New Orleans, named after the Duc d'Orléans, was described by Father Roulleaux de la Vente as "a little village of about one hundred cabins dotted here and there, a large wooden warehouse in which I said Mass, a chapel in course of construction and two storehouses".

[2] In 1722 Bishop Mornay entrusted the spiritual jurisdiction of the Indians to the Jesuits, who were to establish missions in all parts of Louisiana with residence at New Orleans, but were not to exercise any ecclesiastical function there without the consent of the Capuchins, though they were to minister to the French in the Illinois District, with the Priests of the Foreign Missions, where the superior of each body was a vicar-general, just as the Capuchin superior was at New Orleans.

However, as Mornay was named coadjutor with right of succession, He became, de facto, Bishop of Quebec immediately upon Saint-Vallier's death, thus, rendering both the later resignation and appointment null and void.

[4] Fearing any confusion a resignation might inspire, Mornay wrote to Archdeacon Louis-Eustache Chartier de Lotbiniere asking him to take possession of the see in his name.