 He campaigned for the national cause under William Wallace and later Robert the Bruce.As Bishop of St Andrews, the most powerful seat in Scotland, Bishop Lamberton along with Bishop Robert Wishart of Glasgow conducted the coronation of Robert the Bruce as King Robert I. Lamberton would go on to have a vital role in the formulation of the Declaration of the Clergy 1310 and the Declaration of Arbroath which would lead to Scottish Independence.During his tenure Lamberton was excommunicated by Rome for his role in the Wars of Independence along with Robert I and the Clergy of Scotland.