After the Battle of Crecy, the English rested for two days and buried the dead. The English, requiring supplies and reinforcements, marched north. They continued to devastate the land, and razed several towns, including Wissant, the normal port of disembarkation for English shipping to north-east France. Outside the burning town Edward held a council, which decided to capture Calais. The city was an ideal entrepôt from an English point of view, and close to the border of Flanders and Edward's Flemish allies. The English arrived outside the town on 4 September and besieged it.

Calais was strongly fortified: it boasted a double moat, substantial city walls, and its citadel in the north-west corner had its own moat and additional fortifications. It was surrounded by extensive marshes, some of them tidal, making it difficult to find stable platforms for trebuchets and other artillery, or to mine the walls. It was adequately garrisoned and provisioned, and was under the command of the experienced Jean de Vienne. It could be readily reinforced and supplied by sea. The day after the siege commenced, English ships arrived offshore and resupplied, re-equipped and reinforced the English army. The English settled down for a lengthy stay, establishing a thriving camp to the west, Nouville, or "New Town", with two market days each week. A major victualling operation drew on sources throughout England and Wales to supply the besiegers, as well as overland from nearby Flanders. A total of 853 ships, crewed by 24,000 sailors, were involved over the course of the siege; an unprecedented effort. Wearied by nine years of war, Parliament grudgingly agreed to fund the siege. Edward declared it a matter of honour and avowed his intent to remain until the town fell. Two cardinals acting as emissaries from Pope Clement VI, who had been unsuccessfully attempting to negotiate a halt to hostilities since July 1346, continued to travel between the armies, but neither king would speak to them.

On 17 July Philip led the French army north. Alerted to this, Edward called the Flemings to Calais. On 27 July the French came within view of the town, 6 miles (10 km) away. Their army was between 15,000 and 20,000 strong; a third of the size of the English and their allies, who had prepared earthworks and palisades across every approach. The English position was clearly unassailable. In an attempt to save face, Philip now admitted the Pope's emissaries to an audience. They in turn arranged talks, but after four days of wrangling these came to nothing. On 1 August the garrison of Calais, having observed the French army seemingly within reach for a week, signalled that they were on the verge of surrender. That night the French army withdrew. On 3 August 1347 Calais surrendered. The entire French population was expelled. A vast amount of booty was found within the town. Edward repopulated the town with English settlers.

Calais provided the English with an important strategic lodgement for the remainder of the Hundred Years' War and beyond. The port was not recaptured by the French until 1558.