On 5 August 1756, having at that time a license
ad practicandum from the university of Cambridge, Warren was elected a physician to the
Middlesex Hospital, and on 21 January 1760 he became physician to
St. George's Hospital. The former appointment he resigned in November 1758, the latter in May 1766. Warren was admitted a candidate of the
Royal College of Physicians on 30 September 1762.
Sir Edward Wilmot, then physician to the court, recommended Warren to assist him in attending on
Princess Amelia. When Wilmot retired, Warren continued to act as physician to the princess, and then by her influence he was appointed physician to the king on the resignation of Shaw. He was elected a Fellow of the College of Physicians on 3 March 1763. He delivered the
Gulstonian lectures at the College in 1764 and the
Harveian oration in 1768. He acted as censor in 1764, 1776, and 1782. On 9 August 1784 he was named an elect. He became a Fellow of the
Royal Society in 1764. In 1787 Warren was appointed physician to the
Prince of Wales, who sent him to attend the king during his first period of 'madness' in 1788–89. His medical career then brought financial rewards not previously seen in England. He died at his house in
Dover Street on 22 June 1797. He was buried in
Kensington parish church on 30 June 1797.
Elizabeth Inchbald composed mourning verses to his memory. ==Works==