John Stewart, Earl of Buchan (c. 1381 – 17 August 1424) is a Scottish nobleman and soldier who fights alongside Scotland's French allies during the Hundred Years War.

In 1419 he is sent to France by his father the Duke of Albany, Regent of Scotland, with an army of six thousand men.

Stewart leads the combined Franco-Scottish army at the Battle of Baugé on March 21, 1421, where he comprehensively defeats the English forces, proving that the English could at last be beaten.

However, two years later, Stewart is defeated and captured by Thomas Montacute, 4th Earl of Salisbury at the Battle of Cravant in 1423.

After the battle he is exchanged, and after his release in 1424 he is appointed Constable of France, making him the effective Commander-in-Chief of the French army.

On August 17, 1424, Buchan is killed at the disastrous Battle of Verneuil, along with most of the Scottish troops in France.