William Herbert, 1st Marquess of Powis, KG, PC (1626 – 2 June 1696) was an English nobleman, best remembered for his suffering during the Popish Plot.

[2] He was one of the "Five Catholic Lords" falsely accused by Titus Oates in the Popish Plot of conspiring to kill the King and as a result spent six years in the Tower of London awaiting trial; his wife's desperate efforts to free him led her to fabricate the "Meal-Tub plot" for which she narrowly escaped being convicted for treason herself.

He remained in Ireland until the king's flight back to France after the Battle of the Boyne, and settled again at the exiled Jacobite Court at St Germain.

His wife continued as Principal Lady of the Bedchamber to Queen Mary of Modena and Royal Governess to James, Prince of Wales until her death on 11 March 1691.

[4] Together, they had six children, a son and heir and five daughters, one of whom, Winifred, married William Maxwell, 5th Earl of Nithsdale, who was condemned to death for high treason for participating in the Jacobite rising of 1715.