While styled Count of Castres, he served under Charles VII of France in Normandy in 1449 and 1450, and afterwards in Guienne. Louis XI awarded him with honours. In 1462, Jacques succeeded his father, and Louis XI married him to his god-daughter, Louise of Anjou, daughter of Charles of Le Maine. Louis XI also recognized his title to the duchy of Nemours, which he had disputed with the King of Navarre.
Sent by Louis to pacify Roussillon, Nemours felt that he had been insufficiently rewarded for the rapid success of this expedition, and joined the League of the Public Weal in 1465. Subsequently, he reconciled with Louis, but soon resumed his intrigues. After twice pardoning him, the king's patience became exhausted, and he besieged the duke's chateau at Carlat and imprisoned him. Nemours was treated with the utmost rigour, being shut up in a cage. He was finally condemned to death by the parlement and beheaded, 4 Aug 1477.
He and Louise had six children:
- Jacques (d. young)
- Jean d'Armagnac, Duke of Nemours (1467–1500)
- Louis d'Armagnac, Duke of Nemours (1472–1503)
- Marguerite d'Armagnac, Duchess of Nemours (d. 1503), married Peter de Rohan (d.1514)
- Catherine d'Armagnac (d. 1487), married John II, Duke of Bourbon in 1484
- Charlotte d'Armagnac, Duchess of Nemours (d. 1504), married Charles de Rohan (d.1504)
- de Commynes, Philippe and Jean de Roye, The Memoirs of Philip de Commines, Lord of Argenton, (George Bell and Sons, 1873), 16.
- One or more of the preceding sentences incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Nemours, Lords and Dukes of, s.v. James of Armagnac, duke of Nemours". Encyclopædia Britannica. 19 (11th ed.). Cambridge University Press. p. 370.
Bernard II with Eleanor
|Duke of Nemours
Count of Castres, La Marche and Pardiac
|to royal domain|
Charles of Le Maine
|Count of Beaufort-en-Champagne|
With: Louise of Anjou