The seneschal of Poitu was the son of Sir William Felton of Northumberland. The younger Sir William took part in the battle of Halidon Hill in 1333 and the subsequent capture of Berwick. In 1334, he was governor of Bamburgh castle and was active along the border with Scotland. In 1342, he became sheriff of Northumberland and governor of Newcastle.
Felton was at the famous naval battle of Sluys in 1340, as well as the sieges of Tournai and Nantes. He took part in the great victory at Crecy and was with the Black Prince in Poitiers. He became seneschal of Poitu in about 1360. Felton was engaged in numerous combats in Guyenne in 1364 and 1365, and accompanied the Black Prince on his Spanish campaign to restore Don Pedro to the throne of Castile. The chronicler makes frequent mention of 'Felleton Guilliam qui ot coeur de lyon.' William was killed in a skirmish before the Battle of Navarette where his kinsman Sir Thomas Felton was taken prisoner. The heroic exploits of a handful of Englishmen still lives in local legend and the mound where they fought is still known in the local dialect as Inglesmundi, the Englishmen's mound.
According to Dugdale, Sir William had a son, Sir John, who was with Hotspur at the battle of Otterburn in 1388.