William FitzWilliam (Lord Deputy) William FitzWilliam (Lord Deputy) Sir William FitzWilliam (1526–1599) was an English Lord Justice of Ireland and afterwards Lord Deputy of Ireland. In 1587, as Governor of Fotheringhay Castle, he supervised the execution of the death sentence on Mary, Queen of Scots. He was the Member of Parliament for Peterborough and represented County Carlow in the Irish House of Commons. He lived at Gainspark, Essex, and Milton Hall. FitzWilliam was born at Milton Hall, Northamptonshire, the eldest son of Sir William (d. 1576) and grandson of William Fitzwilliam, Sheriff of London, who had been treasurer and chamberlain to Cardinal Wolsey and
Fotheringhay Castle with Edward IV of England to supplant his brother on the throne of Scotland. Mary, Queen of Scots, who had spent much of her 18 years of imprisonment at Sheffield Castle and Sheffield Manor, spent her final days at Fotheringhay, where she was tried and convicted of treason. In this time it was used as a state prison. She attended her own trial in the Great Hall on October 5, 1586, where it lasted two days. After waiting over two months for Elizabeth I of England to officially sign her death warrant, Mary was only given the verdict the day