William Fitz Thomas

William Fitz Thomas was Prior of the Hospitallers at Kilmainham from 1420 to 1438. He also served twice as Lord Chancellor of Ireland; there is some confusion as to the dates of his terms of office, but he is first recorded as holding office as Chancellor in 1415, and stepped down after 1426. In 1417 he witnessed an important charter of King Henry V of England, guaranteeing the liberties of the citizens of Dublin.

Despite his high offices, he was to some extent under the control of the Archbishop of Armagh, in particular as regards his Order's substantial lands in County Louth. The formidable John Swayne, Archbishop of Armagh from 1418 to 1439, was quick to assert his authority: he ordered Fitz Thomas to remove a vicar who was guilty of adultery, He had ceased to be Prior by 1438.