Lucy Hay, Countess of Carlisle (née Percy; 1599 – 5 November 1660), was an English courtier known for her beauty and wit. She was involved in many political intrigues during the English Civil War.
She was born Lady Lucy Percy, the second daughter of Henry, Earl of Northumberland (the famous "Wizard Earl") and his wife Lady Dorothy Devereux. In 1617, she became the second wife of James Hay, 1st Earl of Carlisle. Her charms were celebrated in verse by contemporary poets, including Thomas Carew, William Cartwright, Robert Herrick and Sir John Suckling, and by Sir Toby Matthew in prose.
In 1626, she was appointed Lady of the Bedchamber to Henrietta Maria, Queen of England. She soon became a favorite of the Queen, and participated in two of her famous masque plays.
She was a conspicuous figure at the court of King Charles I. A contemporary scandal made her the mistress successively of Thomas Wentworth, 1st Earl of Strafford, and of John Pym, his parliamentary opponent. Strafford valued her highly, but after his death in 1641, possibly in consequence of a revulsion of feeling at his abandonment by the court, she devoted herself to Pym and the interests of the parliamentary leaders, to whom she communicated the king's most secret plans and counsels.
Her greatest achievement was the timely disclosure to her cousin Robert Devereux, 3rd Earl of Essex, of the King's intended arrest of the five members of the Long Parliament in 1642, which enabled Essex and the others to escape. However, she appears to have served both parties simultaneously, betraying communications on both sides, and doing considerable mischief by inflaming political animosities.