French ecclesiastical historian who was one of the earliest scholars to provide a rigorous appraisal of preceding historical writing. His works were objective and among the first of modern historical works to include a critical discussion of the principal sources for each period.

The son of a wealthy lawyer, Tillemont attended Port-Royal, the famous school of the Jansenists, who advocated an austere form of Roman Catholicism. He began his researches early (1655), scrupulously collecting literary and historical information concerning early Christianity. After entering the seminary at Beauvais (1661), Tillemont collaborated in publishing an edition of the writings of the Church Fathers (1669). In 1667 he took up residence at Port-Royal, becoming chaplain (1675) and later priest (1676). The Jansenist persecutions of 1679 forced him to settle on the family estate of Tillemont, where he remained, continuing his studies in church history until his death.

Tillemont's writings began to appear during his lifetime; the Mémoires pour servir à l'histoire ecclésiastique des six premiers siècles, 16 vol. (1693–1712; “Memoirs Useful for the Ecclesiastical History of the First Six Centuries”), and Histoire des empereurs, 6 vol. (1690–1738; “History of the Emperors”), were originally conceived as one work but were published separately. These books deal with the history of the Christian church and the Roman Empire to about AD 515, giving highly objective accounts as well as citing original sources. They were among the chief sources used by the English historian Edward Gibbon in his Decline and Fall of the Roman Empire.