On 26 January 1357, King David II created him Earl of Douglas.
However, he faithfully supported the cause of national independence, and even went so far as to unite with the Steward and the Earl of March in a formal bond to compel King David to change his counsel lords and to give up his intrigues for altering the succession to the crown in favour of one of the sons of the English king. 
In 1363 he made a pilgrimage to the shrine of St.Thomas-a-Becket; but unlike some others of the great Scottish barons, who made such pilgrimages a pretext for treasonable intrigues with the English Government, Douglas continued steadfast in his adherence to his country's cause and resolutely opposed the attempts of the unworthy son of Robert Bruceto betray it to the enemy. 

On the accession of Robert II, the son of the Steward and Marjory Bruce, the Earl of Douglas unexpectedly put forth pretensions to the crown, but abandoned them on finding that they were not likely to meet with public support. As a reward for the promptitude of his submission, the King's eldest daughter was promised in marriage to his eldest son, and the Earl himself was appointed Justiciar of Scotland south of the Forth, and Warden of the East Marches. 
This great noble, one of the best of his race, died in 1384 at an advanced age. He was succeeded by his eldest son from his wife the Countess of Mar. 

Source: The Great Historic Families of Scotland, by James Taylor, 1889.