He was the eldest son of Sir Guylford Sligsby, Comptroller of the Navy (died 1631) and Margaret Water or Walter of York. His father was one of the many children of Sir Francis Slingsby and Mary Percy, sister of Henry Percy, 8th Earl of Northumberland. He grew up at Bifrons in Canterbury, where his father, originally from Scriven, had purchased an estate. He was educated at the University of St Andrews. Several of his younger brothers also achieved a measure of fame, including Sir Robert Slingsby, 1st Baronet, like his father Comptroller of the Navy and friend of Samuel Pepys, and Arthur, the first of the Slingsby Baronets of Bifrons.
Secretary to Strafford
About the same time he entered Parliament, he entered the Lord Deputy's household as personal secretary. It is possible that his cousin Algernon Percy, 10th Earl of Northumberland, who was then one of Strafford's closest friends, recommended him. He proved an excellent secretary and also became a friend. When Strafford was impeached, he asked Slingsby to join him in London, and throughout the trial which ended in Strafford's attainder and execution, Slingsby provided invaluable support, as well as giving evidence on his behalf. There were unconfirmed reports that Slingsby had attempted to arrange Strafford's escape from the Tower of London.
It has been suggested that Slingsby may have been part author of the Brief and Perfect Relation of the Answers and Replies of Thomas Earl of Strafford to the Articles exhibited against him by the House of Commons, published in 1647.
Friendship with Strafford
Strafford's affection and regard for Slingsby are clear from his final letter to him:
Keep out of the way till I be forgotten and then your return may be with safety...God direct and prosper you in all your ways; and remember there was a person whom you were content to call master that did very much value and esteem you and carried to his death a great stock of his affections for you.
He fled to the Netherlands but soon returned. In 1642 he raised a regiment for King Charles's service but in January 1643 he was defeated at Guisborough by Sir Hugh Cholmeley, wounded and taken prisoner. His legs were amputated and he died shortly afterwards from his wounds. He was buried in York Minster; the funeral sermon was preached by John Bramhall, Bishop of Derry.
- Wedgwood, C.V. Thomas Wentworth, 1st Earl of Strafford 1593-1641- a revaluation Phoenix Press reissue 2000 pp.337-8
- Betham, William Baronetage of England London 1805 Vol. 5 p.26
- Betham p.26
- Guildford Slingsby at Oxford Dictionary of National Biography
- Wedgwood p.338
- Wedgwood p.384