In 1500 he was clerk of the Register, and in 1504 King James IV presented him archdeacon of the diocese of St Andrews.

In 1507 Gavin was sent on a diplomatic mission to Louis XII of France with Antoine d'Arces[2] They sailed on the Treasurer, but on his return the ship was wrecked and he was captured on the orders of Henry VII of England.

He set about major rebuilding and extension of St Machar's Cathedral.Dunbar's career saw the creation of a huge number of minor ecclesiastical establishments, including two chaplaincies in Elgin Cathedral, a hospital in the Chanonry, Old Aberdeen and an altar dedicated to St Katherine in the Aberdeen Cathedral.

To the cathedral, Bishop Dunbar added many structures, including the new south transept.

Due to curtailment of the church the actual grave is now external, within an enclosure made of the original lower eastern walls.