Sir Thomas Grey (30 November 1384 – 2 August 1415), of Heaton Castle in the parish of Norham, Northumberland,[1] was one of the three conspirators in the failed Southampton Plot against King Henry V in 1415, for which he was executed.

Through his mother, a granddaughter of Margaret, Duchess of Norfolk (d. 1399), Sir Thomas Grey was a descendant of King Edward I.

His paternal grandparents were the soldier and chronicler Sir Thomas Grey of Heton, and Margaret, daughter and heiress of William de Pressene of Presson.

[11] By August 1404 he had been retained for life by Ralph Neville, 1st Earl of Westmorland, but by May 1408 was in the service of Henry, Prince of Wales.

[17] The Southampton Plot is dramatized in Shakespeare's Henry V, and in the anonymous play, The History of Sir John Oldcastle.