Scottish statesman and staunch supporter of Mary Stuart, Queen of Scots. In the conflict between Scotland's Protestant nobility and the Roman Catholic Mary, Maitland often defied the queen when her actions threatened to undermine her chances of remaining in power. His overriding aim was to unite the realms of England and Scotland by securing for Mary recognition as successor to England's Queen Elizabeth I.

In 1558 Maitland became secretary to the Roman Catholic pro-French queen regent, Mary of Guise. He soon joined the Protestant lords against the regent, however, in order to help expel the French from Scotland. When Mary Stuart assumed control of the government in 1560, she made Maitland her secretary of state. In order to prod Elizabeth I of England into naming Mary as her successor, Maitland approved of negotiations seemingly intended to result in Mary's marriage to Don Carlos of Spain, an alliance that Elizabeth could not risk. Maitland also had a hand in the unsuccessful proposals of a marriage between Mary and Robert Dudley, earl of Leicester.

Later, Maitland supported the murder (1566) of Mary's favourite, the Italian Catholic David Riccio, who was hated by the Protestant nobles. Maitland may also have had a hand in the murder (1567) of Mary's husband, Henry Stewart, Lord Darnley. He then opposed the queen's marriage (May 1567) to James Hepburn, 4th earl of Bothwell, and joined the coalition of Protestant and Catholic nobles that forced Bothwell to leave Scotland.

After Mary fled to England in May 1568, Maitland remained in Scotland and worked to restore her to power. By promoting her proposed marriage to England's duke of Norfolk in 1570, he broke with the government of James Stewart, earl of Moray, regent for the infant Scottish king James VI. Maitland was arrested but was released upon Moray's death in 1570. In the ensuing civil war he led Mary's supporters against the king's partisans. Maitland held Edinburgh Castle until forced to surrender in May 1573; he died in prison.