In November 1349, Charles de la Cerda, a soldier of fortune, son of Luis de la Cerda, and member of a branch of the Castilian royal family, sailed from northern Spain, commissioned by the French, with an unknown number of ships. He intercepted and captured several English ships laden with wine from Bordeaux and murdered their crews. Later in the year de la Cerda led a Castilian fleet of 47 ships loaded with Spanish wool from Corunna to Sluys, in Flanders, where it wintered. On the way he captured several more English ships, again murdering the crews – by throwing them overboard.

On 10 August 1350, while Edward was at Rotherhithe, he announced his intention of confronting the Castilians. The English fleet was to rendezvous at Sandwich, Kent. Edward had good sources of intelligence in Flanders and knew the composition of De la Cerda's fleet and when it sailed. He determined to intercept it and sailed from Sandwich on 28 August with 50 ships, all smaller than the majority of the Castilian vessels and some much smaller. Edward and many of the highest nobility of England, including two of Edward's sons, sailed with the fleet, which was well provided with men-at-arms and archers.

The Battle of Winchelsea was a naval victory for an English fleet of 50 ships, commanded by King Edward III, over a Castilian fleet of 47 larger vessels, commanded by Charles de la Cerda. Between 14 and 26 Castilian ships were captured, and several were sunk. Only two English vessels are known to have been sunk, but there was a significant loss of life. Charles de la Cerda survived the battle and shortly after was made Constable of France. There was no pursuit of the surviving Castilian ships, which fled to French ports. Joined by French ships, they continued to harass English shipping for the rest of the autumn before withdrawing to Sluys again to winter. The following spring, the Channel was still effectively closed to English shipping unless strongly escorted. Trade with Gascony was less affected, but ships were forced to use ports in western England, often impractically far from their cargo's intended English markets. Others have suggested that the battle was just one of a number of significant and hard-fought naval encounters of the period, only recorded because of the prominent figures involved.