Sarah Jennings, Duchess of Marlborough, also called (1689–1702) Countess of Marlborough, (born May 29, 1660, Sandridge, Hertfordshire, Eng.—died Oct. 18, 1744, London), wife of the renowned general John Churchill, 1st Duke of Marlborough; her close friendship with Queen Anne bolstered her husband’s career and served to aid the Whig cause.

As a child, Sarah Jennings formed a friendship with the Princess Anne (the future queen of Great Britain) and entered the household of Anne’s father, the Duke of York (the future James II) in 1673. Her romance with John Churchill, who was also at court, began late in 1675. Churchill’s parents opposed an unremunerative match, but with the assistance of the Duchess of York the couple were married secretly during the winter of 1677–78. Sarah was devoted to the Princess Anne, who came to depend upon her; they addressed each other as Mrs. Morley and Mrs. Freeman; and, upon Anne’s marriage in 1683, Sarah became one of the ladies of the bedchamber. Sarah escorted Anne to meet the Prince of Orange in 1688 and persuaded her to accept the statutory settlement of the succession. Upon Marlborough’s disgrace in 1692, Queen Mary compelled Anne to dismiss Sarah from her offices and excluded her from court; but after Mary’s death in 1694, Anne and William III were reconciled and the Marlboroughs returned to favour.

After Anne’s accession, the Marlboroughs enjoyed great favour. But Sarah’s favour was in the balance: for the queen had High Church sympathies, while Sarah was a strong Whig. This difference came to a head after 1705; the high Tories had fallen from office but the queen, supported by Robert Harley (later Earl of Oxford), stoutly resisted taking in the Whigs. Sarah persistently urged her to bring the Earl of Sunderland into office in 1706, and mutual irritation showed that the friendship of Anne and Sarah was cooling. Harley was clearly using Mrs. (later Lady) Abigail Masham to supplant Sarah in Anne’s affections by 1707. When Anne’s husband, the Prince of Denmark, died in 1708, relations between Anne and Sarah temporarily improved, but Mrs. Masham’s power grew.

The Whigs and Sarah thoroughly lost influence in 1710. Anne dismissed her, and they never met again. The Marlboroughs settled at Frankfurt am Main in 1713. After the Hanoverian accession they returned to Blenheim, and after the duke’s death in 1722, Sarah completed the building of the palace. She died at Marlborough House in London.