A natural son of Louis, duc d'Orleans, he joined the Armagnacs in the civil war during the reign of King Charles VI and was captured in 1418 by the Burgundians. Released in 1420, he entered the service of the dauphin (later King Charles VII of France) during the Hundred Years War.
Dunois had charge of the defense of Orleans when it was relieved in 1429 by Joan of Arc, joined her subsequent campaign and took part in the coronation of Charles VII. In 1436 he aided in the capture of Paris. He received the county of Dunois from his half brother Charles, duc d'Orleans in 1439. Charles VII later made him count of Longueville.
Dunois was prominent in the conquest of Guienne and Normandy in the final years of the Hundred Years War. He participated in the Praguerie against Charles VII and was a leader of the League of the Public Weal against King Louis XI in 1465, but each time he regained favor at court.