In 1284 he joined with other Scottish noblemen who acknowledged Margaret of Norway as the heir of King Alexander III.
[3] As a descendant of King Donald III, Comyn was one of the thirteen Competitors for the Crown of Scotland.
[3] Comyn, head of the most powerful noble family in Scotland, was a committed ally of Balliol and assisted him in his struggle against Edward I of England.
It has even been suggested that the Comyn family was the driving force behind both the Balliol kingship and the revolt against Edward's demands.
John Comyn as his father was before him was entrusted by King Alexander III with the defence of Scotland's northern territories from invasion by the Vikings and the Danes.