Feeling weak and frequently feverish he joined the royals on their habitual progresses to the Spa towns of the west of England. In 1758 he preached a renowned sermon at London's Guildhall in front of the Duke of Devonshire to inspire the government on the treatment of patients at the Foundling Hospital in St Bartholomew's. He was seen taking the waters at Malvern as early as 1761 for rheumatic pains. Hayter gained preferment as Bishop of London on 19 September 1761, was made a Privy Councillor the same year. He was patronised by Lord Talbot, the Catholic nobleman, who secured his nomination at Bow Church in the East End to be Bishop of London on 24 October 1761 where he was ordained. As the dean of the Chapel Royal his death the following year a post he held until his death on 9 January 1762 at his house in Lisle Street, Leicester Fields, London from dropsy. He was recognised by the erection of a white marble tomb was buried in the churchyard of All Saints Church, Fulham, London on 16 January 1762.