He was born in France, now situated in Val-d'Oise. His mother had leanings toward Protestantism, but his father tried to counteract her influence by sending him to the Collège de Lisieux at Paris. On his father's death in 1559, however, the family formally adopted the reformed faith. Mornay studied law and jurisprudence at the University of Heidelberg in 1565 and the following year Hebrew and German at the University of Padua. During the French Wars of Religion in 1567, he joined the army of Louis I de Bourbon, prince de Condé, but a fall from his horse prevented him from taking an active part in the campaign. His career as Huguenot apologist began in 1571 with the work Dissertation sur l'Église visible, and, as a diplomat in 1572, he undertook a confidential mission for Admiral de Coligny