Louis-Sébastien Le Nain de Tillemont (30 November 1637 – 10 January 1698) was a French ecclesiastical historian.

He was born in Paris into a wealthy Jansenist family and was educated at the Petites écoles of Port-Royal, where his historical interests were formed and encouraged.

At the age of twenty, he began his two monumental works, the Mémoires pour servir à l'histoire ecclésiastique des six premiers siècles and the Histoire des empereurs et autres princes qui ont régné pendant les six premiers siècles de l'Église.

When Port-Royal was dissolved in 1679, he moved to his family estate at Tillemont, where he spent the rest of his life, pursuing his historical work with great devotion.

His work was attacked on a large scale by Honoratus a Sancta Maria in his three-volume Réflexions sur les règles et l'usage de la critique (1712–1720).