In May 1812, he resigned as Attorney General, accepting an appointment as a puisne judge in the Court of Common Pleas. This may have been the result of poor health; Henry Brougham attributed it to personal anxiety after the assassination of Perceval. In any case, Gibbs accepted a great reduction in income to do so, although his appointment as Lord Chief Baron of the Exchequer in November 1813 somewhat eased this. He was, at the same time, sworn of the Privy Council. In February 1814, another promotion made him Chief Justice of the Common Pleas. His tenure there was characterised by a thorough mastery of law, although opinions vary as to whether his temper had by this time been checked. Probably the most celebrated case he heard was the libel action brought by Lady Frances Webster and her husband over the allegation (almost certainly untrue) that she had an affair with the Duke of Wellington. A further decline in health led to his resignation in November 1818, and he died on 8 February 1820 at his house in London, later being interred in the Churchyard of St. Mary the Virgin in Hayes, Bromley.