John Stewart, 4th Earl of Atholl (died 25 April 1579) was a Scottish noble.
Stewart was the son of John Stewart, 3rd Earl of Atholl and Grizel Rattray. He supported the government of the queen dowager, and in 1560 was one of the three nobles who voted in Parliament against the Reformation and the confession of faith, and declared their adherence to Roman Catholicism. Subsequently, however, he joined the league against Huntly, whom with Murray and Morton he defeated at Corrichie in October 1562, and he supported the projected marriage of Elizabeth with Arran.
On the arrival of Mary, Queen of Scots, from France in 1561 he was appointed one of the twelve privy councillors, and on account of his religion obtained a greater share the queen's favour than either Murray or Maitland. He was one of the principal supporters of the marriage with Lord Darnley, became the leader of the Roman Catholic nobles, and with Knox obtained the chief power in the government, successfully protecting Mary and Darnley from Murray's attempts to regain his ascendancy by force of arms. According to Knox he openly attended mass in the queen's chapel, and was especially trusted by Mary in her project of reinstating Roman Catholicism. The fortress of Tantallon was placed in his keeping, and in 1565 he was made lieutenant of the north of Scotland. He was described the same year by the French ambassador as “très grand catholique hardi et vaillant et remuant, comme l'on dict, mais de nul".
After the murder of David Rizzio, in 1567, he joined the Protestant lords against Mary, appeared as one of the leaders against her at Carberry Hill, and afterwards approved of her lavish imprisonment at Loch Leven Castle. In July he was present at the coronation of James, and was included in the council of regency to Mary's abdication. He, however, was not present at Langside in May 1568, and in July became once more a supporter of Mary, voting for her divorce from Bothwell (1569). In March 1570 he formed with other lords the joint letter to Elizabeth asking for the queen's intercession and supporting Mary's claims, and was present at the convention held at Linlithgow in April in opposition to the assembly of the king's party at Edinburgh.