Roman Catholic Scottish noble, sometime supporter of Mary, Queen of Scots.

The son of John Stewart, the 3rd Earl of Atholl in the Stewart line (whom he succeeded in 1542), Atholl was particularly trusted by Mary Stuart; but, after the murder of Mary's husband Lord Darnley in 1567, he joined the Protestant lords against her and, on her abdication, was included in the regent's council for her young son James VI. But he was again advocating her cause by 1569. He failed to prevent the Earl of Morton's appointment to the regency in 1572 but succeeded, with the Earl of Argyll (Argyll, Archibald Campbell, 5th Earl of, Lord Campbell, Lord Lorne), in driving him from office in March 1578, when James dissolved the regency and Atholl was appointed lord chancellor. Morton, however, regained his guardianship of James two months later. Atholl and Argyll, who were seeking assistance from Spain, then advanced to Stirling with a force of about 7,000 men, whereupon a compromise was arranged, the three earls being all included in the government.

After a banquet held on April 20, 1579, to celebrate the reconciliation, Atholl became suddenly ill, and his death on April 24 or 25 may have been caused by poison. On the death in 1595 of his son John, 5th Earl of Atholl, the earldom in default of male heirs reverted to the crown.