Born at Gwennap, Cornwall, in November, 1819, the third son of Dr Michael Williams, of Penponds. He was educated at Swansea Grammar School, then became a pupil of George Gwynne Bird (qv), at one time Mayor of Swansea, and afterwards studied at St Bartholomew's Hospital. He became interested in comparative anatomy, and, after competing unsuccessfully in 1842, was elected Student Assistant at the Royal College of Surgeons on June 19th, 1843. By his diligence and application he won the approval and regard of Professor Owen. Early in 1844 Goadby of the Museum was asked to instruct him in preparing and mounting specimens. The duties of Student Assistant were formulated in the Minutes of the Museum Committee in July, 1846. In the College Library is the MS "Notes of the Work done by John Williams as Student of Anatomy", dated January, 1844. He completed his appointed task in July, 1846, being presented by the Museum Committee with a book, a copy of the Museum Catalogue. On the nomination of the Court of Directors, he accepted an appointment as Surgeon to the HEIC on June 19th, 1847, and went to the Bengal Presidency. He soon made troops of friends, for he possessed sterling qualities both of mind and heart, and he did not come to England again until 1859. He returned to India to serve as Surgeon Major, then as Deputy Inspector of Army Hospitals, with which rank he retired. He then went annually to Norway for the salmon fishing, and on his return in 1877 was found by Caesar Hawkins and Sir James Paget to be suffering from malignant disease of the neck, from which he died after a long course of suffering borne with admirable patience and courage, on May 21st, 1878, at the house of his sister, Mrs Curtis, at Cambridge Park, Redland, Bristol. He never married.