Battle of Towton
Lionel was appointed Lord Lieutenant of Ireland about 1438, and William accompanied him to Ireland, where he acted as his brother's deputy; he was appointed Deputy Lord Chancellor in 1454 and Lord Chancellor of Ireland in 1461. Unlike his brother he does not seem to have been particularly active on behalf of Henry VI, and despite Lionel's death, and the family's strong links to the House of Lancaster, he was still in office a year after the Battle of Towton, which brought about the final downfall of Henry VI. This suggests that the victorious King Edward IV, who was generally magnanimous towards his former opponents, provided that they were prepared to give their loyalty to him, took no action against him. He was killed at the Battle of Towton on 29 March 1461. His main residence was at Posseckstown, near Enfield, County Meath.