The eldest son of Edward Henderson, MD, of Shanghai, he was born in China 18 February 1870, and was educated at Cheltenham College, where he gained a junior classical scholarship in 1882. Two years later he entered Harrow School, when Dr Butler was head master, and remained there until 1887. He then proceeded to St John's College, Cambridge, and graduated BA in 1891, after he had been placed in the second class of Part 1 of the Natural Sciences Tripos. Proceeding to Guy's Hospital he served as house surgeon to C H Golding Bird, and obstetric assistant to Peter Horrocks. He married Hester F Sharpe on 12 January 1897 and returned to Shanghai, where he joined his father in practice and was at once appointed assistant surgeon to the Hospital and to the Shanghai police force. He came back to England in the following year and studied ophthalmology at Moorfields under Sir John Tweedy and William Lang. For fifteen years Henderson worked as clinical assistant at Moorfields and became assistant surgeon in charge of out-patients and pathologist to the Royal Eye Hospital at St George's Circus, Southwark. He was also ophthalmic surgeon to the West Ham Hospital.