Red Comyn was the son of John Comyn, ‘the Black Comyn’, one of the claimants for the Scots throne. His mother was Eleanor Balliol so King John Balliol was his uncle. The Comyns sided with the Balliols and became the enemies of the Bruces.
John Comyn married an English noblewoman, Joan de Valence. Her father was an uncle of King Edward I.
When Scotland was plunged into war, Robert the Bruce’s father was constable of Carlisle Castle under Edward I. The Black Comyn and the Comyn Earl of Buchan attacked Carlisle Castle in support of the Scots King Balliol.
Red Comyn was among the Scots captured at the Battle of Dunbar in 1296. He was imprisoned in the Tower of London. After agreeing to fight for Edward in Flanders, Red Comyn deserted and sailed to Scotland. It is said that he led the cavalry at the Battle of Falkirk. The Scots cavalry at Falkirk were vastly outnumbered by English knights and mounted men at arms. They turned and rode away, leaving the Scots foot soldiers to be slaughtered by Edward I’s army.
Red Comyn was made a guardian of Scotland alongside Robert the Bruce, after the resignation of William Wallace and the death of Andrew Moray. In 1299, at a council in Peebles, a fight broke out between Comyn and Bruce - it was reported that Comyn grabbed Bruce by the throat. Within a year Bruce had resigned the guardianship.
When his father, the Black Comyn, died, John Comyn became Lord of Badenoch.
In February 1303, Red Comyn and Sir Simon Fraser defeated three successive English forces at the Battle of Roslin. It is said that Wallace may have fought at the battle. The Scots drove the English knights over the steep sides of Roslin Glen and cut down their English prisoners as a second then a third force arrived. In 1304 Red Comyn was forced to make peace with Edward I.
On 10 February 1306, Robert the Bruce and the Red Comyn fought by the high altar at Greyfriars Kirk in Dumfries. Comyn was killed and Bruce went on to become king.