His administration was marked by zeal and success along the lines of popular education, training of clerics, parochial organization, restoration of ecclesiastical discipline and extirpation of Protestantism from the Sedan district.

As secretary of the Petite Assemblée of 1681, he reported for the king and against the pope on all disputed points: the extension of the royal claim called régale, the forcible placing of a Cistercian abbess over the Augustinian nuns of Charonne, and the expulsion of the canonically elected vicars capitular of Pamiers.

Elected president with Harlay, he caused the bishops to endorse the royal policy of encroachment on church affairs, and even memorialized the pope with a view to make him accept the régale.

As president of the Assembly (1700) which undertook to deal with Jansenism and Laxism already judged by the pope, Le Tellier was lenient with the Jansenists and severe with theologians of repute.

Le Tellier is remembered as a successful administrator, an orator of some merit, a promoter of letters, a protector of Saint John Baptist de la Salle, Mabillon, Ruinart, etc., and a bosom friend of Bossuet, whom he consecrated, and visited on his deathbed, and whom he induced to write the "Oraison funèbre de Michel Le Tellier."