England at the council of Constance, and on 16 Nov. Sir William Lisle, jun., was appointed his lieutenant to supply his place at Calais during his absence. The splendour of the English embassy at the council is said to have excited general admiration and astonishment. The earl appears, however, to have returned to England pretty early next year, as we find him at the Blackfriars in London on 21 May (Rymer, ix. 319). In August he accompanied the king in the invasion of France; but after the siege of Harfleur the king sent him home again, along with his brother Clarence, in charge of a number of prisoners and a quantity of the spoils of war (Monstrelet, i. 226).
It is said that when he was appointed deputy of Calais the French were expected to besiege the place; but that when he found their forces were bent in a different direction he caused some new feats of chivalry to be instituted, of which a curious description may be seen in Dugdale. In 1416 he received the Emperor Sigismund at Calais on his way to England, and also conducted the Duke of Burgundy to Calais to a conference with Henry V. Next year he was appointed to receive the surrender of Caen Castle. So great was Henry's confidence in his military skill that he divided the chief commands in Normandy between himself, his brother Clarence, and the Earl of Warwick. In 1418 he won Domfront from the French, and joined the king at the siege of Rouen. Dugdale's statement, that he was sent to besiege Nully Levesque, is clearly an error, owing to a misreading of Walsingham's words, who really says that the Earl of Kyme was despatched on that mission. While the English army lay before Rouen the Dauphin made overtures for peace, and Warwick, along with other commissioners, was appointed to discuss matters with his deputies (Rymer, ix. 626). But these negotiations took no effect. In January 1419 Warwick was the principal commissioner to receive the capitulation of Rouen; after which he was again employed in frequent negotiations, not now with the dauphin's party, but with the Burgundian faction, who had charge of the imbecile king (Rymer, ix, 717, 750-1, 774-5, 782, 813). He arranged the truce preparatory to the treaty of Troyes and the marriage of Henry V to Katharine of France. It was presumably on the capture of Aumarle, or Aumale, in Normandy, this year, that the king granted him the additional title of earl of Aumarle, which he bore in his later years. In 1420 he besieged and took Melun. He returned to England with the king in 1421, and acted as deputy to the Duke of Clarence, steward of England at Queen Katharine's coronation. In 1422 he was one of the commissioners appointed to receive the surrender of Meaux, and assisted in the rescue of the Duke of Burgundy's city of Cosne when it was besieged by the dauphin.
That same year Henry V died. So great had been the confidence he reposed in Warwick that he bequeathed to him the care of the education of his infant son, Henry VI, and his wishes were complied with by the council a few years later. On 10 July 1423 his commission as captain of Calais was renewed for two years dating from 4 Feb. preceding. Yet he appears to have resided chiefly in England for several years as member of the council during the king's minority. On 1 June 1428 the council gave him a formal commission under the great seal to take charge of Henry's education — a task in which four years later he demanded special authority to chastise his pupil when necessary, and to remove from his presence any associate whose influence might not tend to improve him. In 1429, at Henry's coronation at Westminster, he bore the king to church. In 1430 he went to Edinburgh, and arranged a truce with Scotland. Next year he was again in Normandy, and took a notable prisoner named Poton de Xaintrailles beside Beauvais. But we find him at Westminster again in August 1433 (Rymer, x. 555). He made his will at Caversham, in Oxfordshire, 8 Aug. 1435. Next year he crossed the Channel to protect Calais from a threatened siege by the Duke of Burgundy; and in 1437 (having meanwhile returned to England) he was again sent over sea, being appointed on 16 July lieutenant of France and Normandy, and discharged by the council of the care of the king's person. It was the most serious responsibility he had yet undertaken; for the English dominion in France was even then manifestly giving way, and though his predecessor, the Duke of York — who was now to be withdrawn — had achieved some marked success, he had been very ill supported. Warwick accordingly took care to make special conditions touching his appointment, and particularly stipulated that if those conditions were not fulfilled he might return without blame (Stevenson, Wars of the English in France, ii. lxvi-lxx). He set sail from Portsmouth on 29 Aug., and remained in France till his death, which occurred at Rouen on 30 April 1439, hastened, in all probability, by the grave anxieties of his position. His body was brought home and buried at Warwick, where his magnificent tomb and efiigy are still to be seen in a chapel attached to the collegiate church of