St Elmo Nelson was born 18 March 1919, the son of the late Dudley Nelson and Dorothy Maida (née Browne), of Highton, Victoria, Australia; he was educated first privately, then at Geelong School, Oxford University and the Sorbonne [Paris, France]. In 1958 he married Lynette Margaret, only daughter of the late Phillip Anthony Browne, of Yarram and Frankston, Victoria, Australia.

During the war of 1939-45 (despatches), Nelson served in 2/7 Australian Infantry Battalion (Major); campaigns in North Africa, Greece, Crete, New Guinea [later Papua New Guinea and part of Indonesia]; Instructor Staff College, Cabalah, 1944. After the war, Dudley joined the British Colonial Administrative Service in Nigeria, as: Cadet 1947; Administrative Officer (Class II), 1957; Resident, Plateau Province, 1961; Resident and Provincial Secretary, Kabba Province, 1962; Provincial Secretary, Kano Province, 1963-67, Sokoto, 1967-68. Chairman, Committee which divided assets of Northern Region between the six Northern States, 1967; Permanent Secretary, Military Governor’s Office, Kano, 1968-76; Acting Secretary to Military Government, and Head of Kano State Civil Service, 1970, 1973 and 1975; Election supervisor, Rhodesian independence elections, 1980.

He was awarded the CMG in 1964.