Along with his nephew, Archibald Douglas, 5th Earl of Douglas, he sat on the jury which convicted Murdoch and two of his sons of treason for failure to pay the ransom and allowing the king to be imprisoned for 18 years. In 1426 as a reward for his loyalty Douglas received royal confirmation of his lands and his eldest son William was knighted in 1430. By 1435 he was made sheriff of Lanarkshire, further strengthening his place among the king's principal followers.
He sat on a jury with Archibald Douglas, 5th Earl of Douglas, to convict Murdoch and two sons of treason for failing to pay ransom and allowing the king to be imprisoned for eighteen years. In 1426, as a reward for his loyalty, Douglas received royal confirmation of his lands. His eldest son, William, was knighted in 1430. By 1435, he became sheriff of Lanarkshire, further cementing his position among the king's principal followers.