John Henry Singleton Pettit was consultant dermatologist and leprologist based in Malaysia. He was born in London, the son of William John Pettit, a teacher, and Rebecca Winifred Blanch née Barron. He was educated at Bruce Grove School in Tottenham and then Richmond County School. He went on to study medicine at Westminster Hospital, London.

He held an appointment as a house physician at Dulwich Hospital and was then a senior casualty officer at Westminster Hospital. Between 1947 and 1949 he was an acting surgeon lieutenant in the RNVR. He then held posts as a graded registrar at Liverpool United Hospitals and St John’s Hospital for Diseases of the Skin from 1950 to 1959, spending a year in Leeds from 1953 to 1954 as an MRC research fellow. From 1954 to 1958 he was a surgeon lieutenant in the RNVR (Merseyside division).

In 1959 he was appointed as professor of dermatology at the University of Tabriz, Iran. A year later he moved to the University of Shiraz, also in Iran. In 1962 he went to Malaysia, where he was director of the MRC leprosy research unit, Sungei Buloh. He later became a consultant dermatologist at Lady Templar Hospital, Kuala Lumpar, among other posts. He was a medical adviser to Selangor Red Cross, Malaysia, from 1966 onwards.

Outside medicine he was an enthusiastic traveller and was interested in the theatre, becoming director of Kuala Lumpa Theatre Workshop from 1968. He remained unmarried.