He had succeeded his father as the second Lord Dalzell in 1636, and was made a Privy Counsellor of Scotland in June 1638.
He was fined £10,000 and his titles were forfeited and he was sentenced to death by an Act of the Scottish Parliament on 25 Feb 1645.
This Act also provided "that his lawful son Gavin, Lord Dalzell, shall enjoy not only all the estates but the title of Earl as if his father were dead".
Carnwath's action was misinterpreted by the royalist soldiers as a signal to move back, leading to a collapse of their position.
[4] Lord Carnwath was taken prisoner after the Battle of Worcester 1651, and committed to the Tower of London for a time.