Sir Nicholas Bagenal[a] (/ˈbæɡnəl/; c. 1509 - February 1591) was an English soldier and politician who became Marshal of the Irish Army during the Tudor era.

[b] He was the second son of John Bagenal (died 1558), a tailor who served as Mayor of Newcastle-under-Lyme, by his wife Eleanor Whittingham of Middlewich, Cheshire.

[4] In 1538, Nicholas fled to Ireland to escape justice for killing a man in the Staffordshire village of Leek; his two brothers were apparently also involved in this crime.

[5][6][7] The Bagenals had family links with the Irish government through Sir Patrick Barnewall, who was the Master of the Rolls in Ireland and married to Anne Luttrell, a cousin of Nicholas.

Bagenal's patent was dated 5 October 1565, but he had scarcely taken up the office when, early in 1566, he entered into an agreement to sell it and his lands to Sir Thomas Stukley who was a close friend of the Pope.

Sir Nicholas was appointed chief commissioner on 6 July 1584 for the government of Ulster, and in April 1585 he was returned to the Irish Parliament as member for County Down.

His son Henry was killed during the greatest defeat the English suffered in Ireland at the Battle of Yellow Ford in County Armagh on 14 August 1598 in action against his brother-in-law Tyrone.

Mabel eloped with Hugh O'Neill, 2nd Earl of Tyrone; she became one of the most romantic figures in Irish history, being described as "the Helen of Troy of the Elizabethan Wars".

Mabel and her sister Mary Barnewall are major characters in the play Making History by Brian Friel; their father and brother Henry are frequently referred to but do not appear on stage.