FitzWalter gained a reputation as a good soldier during Edward III's early campaigns, and he periodically returned to fight in France over the course of his career. In 1346, for example, no longer serving under Northampton, he served with the Prince of Wales, with whom FitzWalter indentured to serve for six months at a wage of 100 marks. In return he brought the Prince 20 men-at-arms (himself, four other knights and 15 esquires) and 12 archers. As part of the Black Prince's vanguard FitzWalter fought at the siege of Calais in 1346. He was by now an experienced soldier and had been made a knight banneret. He was still on campaign in France in 1348, by which time he had returned to Northampton's service.