Agnes Leslie, Countess of Morton

Agnes Leslie, Countess of Morton (born after 1541 – c. 1606) was a Scottish noblewoman, being the daughter of George Leslie, 4th Earl of Rothes as well as a direct descendant of King James II in her maternal line. She was the wife of William Douglas, 6th Earl of Morton, who as Laird of Lochleven Castle was the custodian of Mary, Queen of Scots during her captivity from June 1567 until her escape on 2 May 1568. Agnes was Queen Mary's chief female companion throughout her imprisonment; thus it was while Lady Agnes was recovering from childbirth that the queen successfully escaped from Lochleven.

Lady Agnes was born sometime after 1541 in Scotland, the daughter of George Leslie, 4th Earl of Rothes, Ambassador to Denmark (died 28 November 1558), by his marriage to Margaret Crichton, whom he married twice. Agnes had three sisters and two elder brothers, William and Norman Leslie, Master of Rothes whose rights of inheritance were forfeited as a result of both having been implicated in the murder of Cardinal Beaton in 1546. Her father was also tried and acquitted of the same crime. She had several half-siblings, including Andrew Leslie, 5th Earl of Rothes, her father's son by his marriage to Agnes Somerville.

Her paternal grandparents were William Leslie, 3rd Earl of Rothes and Janet Balfour, and her maternal grandparents were William Crichton, 3rd Lord Crichton of Auchingoul and his mistress, Princess Margaret Stewart, youngest daughter of King James II of Scotland and Mary of Guelders.

Agnes's father died in 1558 in Dieppe, France while on a diplomatic mission.

On 26 November 1554 she married Sir William Douglas, Laird of Lochleven. The contract for their marriage was signed on 19 August 1554. Sir William was the son of Sir Robert Douglas and Margaret Erskine, a former mistress of King James V of Scotland. Sir William's half-brother from his mother's liaison with the king was James Stewart, Earl of Moray, Regent of Scotland from 1567 until his assassination in January 1570. Sir William's cousin was another Regent of Scotland James Douglas, 4th Earl of Morton. The couple made their home at Lochleven Castle, which was a fortress situated on an island in the middle of the loch, and where his widowed mother also resided.