After the death of his father King Philip VI of France ordered him to be educated together with the children of the Duke of Normandy.
Barbara Tuchman postulated that they both refused the office because they knew the King was ailing and a regency under the Dukes of Anjou, Berry and Burgundy was coming and they didn't want the political enmity the function brought with it.
When Louis II of Flanders was driven out of his county by the revolt of Ghent, Sancerre was part of the royal army that was raised to put down the rebellion.
At the Lys River near the town of Comines, the French army was held up by 900 Flemish soldiers commanded by Peter van den Bossche.
Soon the bridge was rebuilt, the bulk of the French army crossed and the superior force quickly put the Flemish spearmen to flight.
In 1387, Louis de Sancerre drove the English out of the castle of La Rochandry and besieged Châteauneuf-sur-Charente, Vibrac and Merpins.
In 1398 Sancerre lead an army against the captal de Buch and the count of Foix and, after a campaign during which he took several towns and castles, successfully negotiated with them to leave the English camp and to submit to the French King.