Comyn was from one of the most important noble families of Scotland. They were arch-rivals of Bruce for the Scottish crown. Comyn’s great-uncle was John Balliol, who had been chosen as king of Scotland back in 1292 and his father had been Guardian of Scotland jointly with William Wallace and then with Bruce.
After his father was murdered by Bruce in in 1306, the young Comyn was taken in by Edward I. In 1314 he was eager to win back his family lands from Bruce and avenge his father’s death.
His wife, the fiercely independent Isabella, Countess of Buchan, was a staunch supporter of Bruce and his cause, and was captured and imprisoned after the battle of Methven along with Bruce’s other female supporters.
Comyn fought and was killed with Pembroke’s men as they escorted the unwilling Edward II from the battlefield of defeat.