Sir Henry Slingsby, first baronet (1602-1658), royalist army officer and conspirator, was born on 14 January 1602, second son of Sir Henry Slingsby (d. 1634) of Scriven, Yorkshire. In the elections to the Short Parliament, Slingsby was returned for Knaresborough. On 20 May 1642 he left London to join the king at York, having been commissioned on 11 May to command the City regiment of the Yorkshire trained bands. On 13 December he was commissioned by the Earl of Newcastle to raise a regiment of foot, which he commanded in the northern campaigns of 1643 and 1644. He was a combatant at Marston Moor, attended the king and the Oxford Parliament in December 1644, and was present at the capture of Leicester and the battle of Naseby. In November 1645 he joined the garrison at Newark, and he was there when it surrendered in the following May.
In July 1646 Slingsby petitioned to compound for his delinquency on the Newark articles, but this offer was rejected. In 1651 he was named in the Act for the sale of delinquents' estates. By 1654 Slingsby was in contact with the royalist underground. Implicated in the northern royalist rising of 1655, he was imprisoned at Hull, where he attempted to subvert several of the garrison officers in a plot to betray the town to the king's forces. The conspiracy was uncovered and on 25 March 1658 Slingsby stood trial for treason before a newly commissioned high court of justice at Westminster Hall. He was found guilty and executed at Tower Hill on 8 June. His body was given to his family, and he was buried in Knaresborough church.
Sir Henry Slingsby's Diary, covering the years 1638 to 1648, is a valuable source for the civil war in northern England, and provides a revealing insight into the mind of an interesting, if not exactly typical, seventeenth-century country gentleman. The work was strongly informed by Slingsby's reading of Montaigne. The diary was edited from the manuscript in 1836 by the Reverend Daniel Parsons and published under the title The Diary of Sir Henry Slingsby of Scriven, bart.(London: Longman, Rees, Orme, Brown, Green, and Longman [etc.], 1836), with notes and additions, including A father's legacy. Sir Henry Slingbey's instructions to his sonnes. Written a little before his death (1658).
Source: David Scott, 'Slingsby, Sir Henry, first baronet (1602-1658)', Oxford Dictionary of National Biography, Oxford University Press, 2004. By permission of Oxford University Press - http://dx.doi.org/10.1093/ref:odnb/25727.