Thomas Percy was the 1605 plotter who rented the undercroft beneath the House of Lords.
Percy was a Catholic gentleman and a member of the household of Henry Percy, 9th Earl of Northumberland. His access to the parliamentary precincts helped the conspirators obtain a lease on the undercroft directly below the House of Lords. The plotters used the space to store the gunpowder intended for the state opening.
Guy Fawkes guarded the explosives there, but Percy’s rental arrangement made the location available. Percy was not present when Fawkes was arrested because he had left London after the warning letter became known. He later joined Catesby in the flight from the authorities.
Percy was killed at Holbeche House on 8 November 1605 alongside Catesby. He is sometimes confused with Thomas Wintour, another principal conspirator, because both men helped organise the plot and both were closely connected to Catesby.