Sir John Steward, lord of Darnley, was a member of a distant cadet branch of the house of Stewart who came to prominence during the Scottish involvement in the fighting in France during the 1420s.
He had succeeded his father as lord of Darnley in 1404, but he was not knighted until 1418-1419, probably during the preparation for the Scottish expedition to France. This was triggered by a French request for help, which reached Scotland later in 1418. The Scots decided to send 6,000 volunteers to France, under the command of John Steward, earl of Buchan, Archibald Douglas, earl of Wigtown, and Darnley. They arrived in France early in 1419, and by 1420 Darnley was being referred to as the constable of the Scottish army in France.
During 1420 the Scottish troops in France saw little action, but that began to change in the following year. Buchan, Wigtown and Darnley were all present at the battle of Baugé on 22 March 1421, which saw a predominantly Scottish army destroy a large part of an English raiding force under the duke of Clarence. Clarence himself was killed in the battle. Darnley was rewarded with the castellany of Concressault in 1421 and the lordship of Aubigny in 1422. 1422 was otherwise a quiet year for Darnley. The year was dominated by the siege of Meaux and the death of Henry V.
1423 would be a much more significant year. Early in the year he commanded a Scottish force that helped to defeat an English column that was heading for Bourges. He was then appointed to command a Franco-Scottish army that was sent to attack the Burgundian fortress of Cravant on the Yonne. The English regent, John duke of Bedford, responded by sending an army under Thomas Montague, earl of Salisbury, to lift the siege. On 31 July 1423 the two armies clashed at Cravant. This time a large part of the Scottish army was destroyed. Darnley lost an eye in the fighting, and was captured by the English.
This period of captivity meant that Darnley missed the disastrous Franco-Scottish defeat at Verneuil on 17 August 1424. At this battle John Stewart, third earl of Buchan and Archibald Douglas, fourth earl of Douglas, were both killed. It is possible that as many as 8,000 Scottish troops were killed at Cravant and Verneuil.
Darnley’s ransom was paid with help from Charles VII of France, and he returned to French service, commanding the remaining Scottish troops in France. In 1426 he took part in a victory over the English at Mont St. Michel, which won him the right to quarter his own arms with the French royal arms. In 1427 he was made count of Evreux.
In 1427 Darnley was part of a embassy sent to Scotland, along with Reynaud de Chartres, archbishop of Rheims. Their mission was to request another 6,000 men, in return for a marriage between Margaret, daughter of James I and the dauphin Louis.
Darnley himself returned to France in January 1429 at the head of a band of volunteers. He made his way to Orléans, where he played a brief but active part in the defence of the city. On 12 February 1429 he was killed in a skirmish at Rouvray, and was buried in the cathedral church at Orléans.
After Darnley’s death his eldest son Alan returned to Scotland, while his second son, John Stewart, remained in France, retaining the title of seigneur d’Aubigny and successfully founding a French branch of the family.