The son of Joseph Ranby of
St. Giles-in-the-Fields in
Middlesex, an innholder, he put himself apprentice to Edward Barnard, foreign brother of the Company of Barber-Surgeons, on 5 April 1715. On 5 October 1722 he was examined on his skill in surgery. His answers were approved, and he was ordered the seal of the
Barber Surgeons Company as a foreign brother. He was elected a
Fellow of the Royal Society on 30 November 1724. He was appointed surgeon-in-ordinary to the king's household in 1738, and in 1740 he was promoted sergeant-surgeon to George II. He became principal sergeant-surgeon in May 1743, and in this capacity accompanied the king in the German campaign of that year. He was present at the
battle of Dettingen, and there had as a patient
Prince William, Duke of Cumberland, the king's second son. from the 1750s, view of John Ranby's house at
Chiswick. In 1745 Ranby's interest with the king and the government of the day helped the passing of the act of parliament constituting a corporation of surgeons distinct from that of the barbers. He was the nominated as the first master of the newly founded surgeons' company, though he had held no office in the old and united company of Barber-Surgeons. Joseph Sandford, the senior warden of the old company, and
William Cheselden, the junior warden, took office under him as the first wardens. He was re-elected master of the company in 1751, when the company entered into occupation of their new theatre in the Old Bailey, and for a third time in 1752. Ranby was appointed surgeon to the
Chelsea Hospital on 13 May 1752 in succession to Cheselden. John Ranby died on 28 August 1773, after a few hours' illness, at his apartments in Chelsea Hospital, and was buried in the south-west portion of the burying-ground attached to the hospital, in a square sandstone tomb with a simple inscription. ==Reputation==