Lieutenant-General Sir William Porter MacArthur KCB DSO OBE FRCP FRCPI (11 March 1884 – 30 July 1964) was an Irish-born British Army officer and medical doctor. He served as Commandant of the Royal Army Medical College from 1935 to 1938, and Director General Army Medical Services from 1938 to 1941. His specialism as a medical doctor was tropical medicine and he served as President of the Royal Society of Tropical Medicine and Hygiene from 1959 to 1961.