French mistress of Charles II of Great Britain, the least popular with his subjects but the ablest politician.

The daughter of a Breton nobleman, Guillaume de Penancoet, Sieur de Kéroualle, she entered the household of Henrietta Anne, Duchess d'Orléans, the sister of Charles II, in 1668 and accompanied her to England in May 1670 for the festivities that disguised the secret Treaty of Dover. The sudden death of the duchess (in June) left her unprovided for, but Charles placed her among the ladies in waiting of his own queen. It was said in later times that she had been selected by the French court to fascinate the king of England, but for this there seems to be no evidence. Yet when there appeared a prospect that the king would show her favour, the French ambassador, Colbert de Croissy, and Lord Arlington, the principal secretary of state, united in promoting her for the sake of French interests, and it was at the latter's country house at Euston, in Suffolk, that the liaison was consummated in October 1671. A son, Charles Lennox, later Duke of Richmond, was born in July 1672.

The support that she received from the French envoy was given on the understanding that she should serve the interests of her native sovereign. The bargain was confirmed by gifts and honours from Louis XIV, who conferred upon her the duchy of Aubigny in 1673. Louise also continued in Charles's favour for many years; her English titles of Baroness Petersfield, Countess of Fareham, and Duchess of Portsmouth were bestowed in 1673, and in 1674 she was assured of an income of at least £10,000 a year. She proved skillful in safeguarding her position through leading politicians such as the earls of Danby, Sunderland, and Shaftesbury and used her considerable influence with the king on their behalf. However, her unequaled rapacity made her unpopular, and in 1678 her Roman Catholic, French connection placed her in some danger during the Popish Plot. Nevertheless she remained close to Charles until his death (Feb. 6, 1685), and she may have assisted in his reception into the Roman Catholic church. Soon after his death she retired to France, where, except for one short visit to England during the reign of James II, she remained. Her emoluments were lost in her later years, which were spent at Aubigny, but she was protected from her creditors by Louis XIV.