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.