Clerk, nephew of the architects Robert and John Adam, was admitted to the Faculty of Advocates in 1785. He became a successful barrister with a reputation for speaking his mind and appeared as a defence lawyer during the trial of Deacon Brodie in 1788. He was appointed Solicitor-General in 1806 and was elevated to the bench as Lord Eldin in 1823. However, he was already infirm and lacked the temperament to be a successful judge; he resigned five years later. Clerk was regarded as a rather eccentric Edinburgh character; he was a keen collector of art and extremely fond of cats, with at least six feline companions. After his death an auction of his possessions was held at his house in Picardy Place. The floor gave way during the sale, causing many injuries and one fatality.