Harrington's father, Sir Nicholas, was a supporter of John of Gaunt and Harrington continued this tradition of service with the future Henry V. He served
Henry V whilst the latter was
Prince of Wales, and when Henry came to the throne in 1413, Harrington was a king's knight. He was considered to be one of the most trusted nobles and, as such, was appointed to hold the official office of
Standard Bearer of England. Some of his predecessors in the role were men like
Peter de Preaux and Richard Fitzhugh. Some of the men succeededing him in the role were men such as Sir Lewis Robessart and Sir William Burton. The role of standard-bearer of England was an important office within an army especially when monarchs fought or were present on the battlefield. On the battlefield, the standard-bearer would be mounted and carried the personal standard of the monarch. In 1415 he fought at the
Battle of Agincourt holding the king's standard, having previously been at the
Siege of Harfleur. In 1416 he served in Henry's campaign to rescue Harfleur and finally on another of Henry V's Normandy campaigns, he was seriously wounded at the
Siege of Rouen (1418–1419) where again he had acted as standard-bearer. For his loyalty and valour at Agincourt, in 1416/17 he was elected (along with fourteen other knights who served at Agincourt) to the
Order of the Garter as a
knight of the Garter. The stall plates of eleven of these knights can be seen in the Quire of
St George's Chapel, Windsor Castle although the remainder no longer survive, perhaps lost in the move from the original St George's Chapel to the current Chapel constructed by
Edward IV of England. Sir William's personal garter number is 123 and on the shield of his garter arms is the
Harrington knot. ==Family==