His early writings show a man who read Jean-Jacques Rousseau and Voltaire, but his ideals were closer to the theories of Montesquieu and the Physiocrats. He was influenced by Cesare Beccaria on the reform of justice. He became the center of the parliamentary strength against absolutism, moving toward positions close to those advocated by Antoine Barnave and Jean Joseph Mounier. He shared the enthusiasm of his contemporaries to the American Revolution, and became acquainted with Lafayette.
From 1784, he was a follower of mesmerism, and saw this secret society a way to prepare for major changes in society and the state. He was friends with Nicolas Berger and Jacques Pierre Brissot. He was initiated at the lodge of the Friends meeting in Paris, and he participated in Freemasonry debates. He became one of the main leaders of the parliamentary group, the Marais.
Elected in 1789, to the states-general by the Paris nobility, he displayed remarkable eloquence. As a jurist, he contributed during the Constituent Assembly to the organization of the judiciary of France. In his report of March 29, 1790, he advocated trial by jury; but failed to introduce the jury system in civil cases.
Duport formed with Barnave and Alexandre de Lameth a group known as the "triumvirate," which was popular at first. But after the flight of King Louis XVI to Varennes, Duport tried to defend him; as member of the commission charged to question the king, he found excuses, and on July 14, 1791 he opposed the formal accusation. Having separated himself from the Jacobins, he joined the Feuillant party. After the Constituent Assembly, he became president of the criminal tribunal of Paris, but was arrested by Danton during the insurrection of 10 August 1792. He escaped, thanks to evidence provided by Jean-Paul Marat, and fled to Switzerland. He returned to France after the 9th of Thermidor of the year II, left it in exile again after the republican coup d'état of 18 Fructidor of the year V, and died at Appenzell in Switzerland in 1798.
- F.A. Aulard, Les Orateurs de la Constituante (2nd ed., Paris, 1905, 8vo).
- From speech made by Danton during his trial, transcribed in Discours de Danton ed. A. Fribourg, SHRF, 1910