Sir William Russell was seated at Yaverland for the remainder of his life and played a central role in the defence of the Island from the frequent attacks by the French. He was appointed as one of three Wardens of the Island and Constable of Carisbrooke Castle, the "caput" of the Island, from which all manors were held under feudal ties. In 1294 he received royal instructions for putting the Island into a proper posture to meet the threatened invasion by France of the southern coasts of England. In 1295, still as a younger son, his brothers being still alive, he was elected to parliament as burgess for Great Bedwyn, Wiltshire, where the Russell family held the manor of Little Bedwyn, apparently acquired by his grandfather John Russell. In 1297 he was summoned by King Edward I to join with his barons to muster in London in preparation for a military expedition crossing over to Flanders. Sir William was summoned by royal writ to be at York on 25 May 1298 to oppose the Scotsman William Wallace. He fought at the Battle of Falkirk, where a great English victory was won. However, the Scottish forces regrouped and Russell was again summoned to join King Edward's army on 24 June 1300 at Carlisle.