Philippe De Mornay, seigneur du Plessis-Marly, known as Duplessis-Mornay, a French soldier, born at Buhy, Isle de France, Nov. 5, 1549, died at Foret-sur-Sevre, Nov. 11, 1623. His father was a Roman Catholic, but his mother secretly brought him up as a Protestant, and after his father's death in 1500 he openly professed that religion. At an early age he travelled extensively, attached himself to Vdmiral Coligni, and drew up a memorial in behalf of the Huguenots, which was presented to Charles IX. and Catharine de Medici. After the massacre of St. Bartholomew s, from which he had a narrow escape, he took refuge in England. He returned in 1575, and Henry of Navarre intrusted to him some important missions to Queen Elizabeth. Being appointed general superintendent of Navarre, he stood almost alone the brunt of the religious civil war. On the alliance of his master with Henry III., he was placed in command of the town of Saumur, assigned as a place of fety to the Protestants. In 1589 he arrested and kept prisoner the old cardinal de Bourbon, whom the leaguers had proclaimed king in opposition to Henry IV. He opposed the abjuration of the latter, and evinced so intemperate a zeal for Calvinism as to incur the king's displeasure.

Nevertheless he kept his governorship of Saumur, where on the death of Henry (1610) he proclaimed the authority of Maria de' Medici; but he quarrelled with that princess, and in 1620 was compelled to resign his office, receiving as indemnity a sum of 100,000 livres. His high character, virtue, and knowledge made him for nearly half a century the chief of the French Calvinists; and he was commonly styled by the Catholics le pape des Huguenots. He left various controversial works, and also his personal Memoires (4 vols. 4to, 1624-'52;'more complete edition by Au-guis, 12 vols. 8vo, 1822-'5). See also Memoires de Madame de Momay, published by Mine. de Witt under the auspices of the French historical society (2 vols., Paris, 1868-'9).