Two portraits of Lucy Hay, Countess of Carlisle, by Anthony van Dyck, 1637

Lucy Hay, Countess of Carlisle, née Percy (1599 - November 5, 1660), English courtier known for her beauty and wit. Her charms were celebrated in verse by contemporary poets, including Thomas Carew, William Cartwright, Robert Herrick, and Sir John Suckling. She was later involved in many conspiracies and political intrigues during the English Civil War.

She was the second daughter of Henry Percy, 9th earl of Northumberland, and his wife Dorothy Devereux. In 1617, she married James Hay (he would become Earl of Carlisle five years later) as his second wife, and became a conspicuous figure at the court of Charles I. After the death of her husband in 1636, she was rumored to have been, successively, the mistress of Thomas Wentworth, 1st Earl of Strafford, and then John Pym, his parliamentary opponent. Strafford valued her highly, but after his death, possibly as a result of her anger and disillusionment at his fall and execution, she devoted herself to Pym and gave herself to the interests of the parliamentary leaders, to whom she communicated the king's most secret plans and counsels. However, it appears she served both parties simultaneously, betraying communications on both sides, and doing considerable mischief by inflaming political animosities.

In 1647 she attached herself to more moderate factions, but by the next year, with second phase of the Civil War, she was again demonstrating great zeal for the royal cause, raising funds for Royalist troops, and making herself intermediary between scattered bands of Royalists and the queen. In consequence, in March 1649, two months after Charles I's execution, her arrest was ordered and she was imprisoned in the Tower. Even in prison, she continued her intrigues, corresponding in cipher with the future Charles II. Royalist reports made out that she was threatened with the rack in order to extort information. She was released in September of the following year, but appears never to have regained her influence, and died ten years later, soon after the Restoration.