His books have included New Guinea: The Last Unknown (1963), a history of the exploration of all the territories of New Guinea, written after he had accompanied an initial penetration patrol making first contact with the Gants people of the Jimi Valley; A Peculiar People (1968), an account of the New Australia Utopian settlement in Paraguay; The Idle Hill of Summer: an Australian Childhood 1939-1945 (1972); Lion & Kangaroo: The Initiation of Australia 1901-1919 (1976).
In 1981 he was commissioned by John Clunies-Ross, "King" of the Cocos (Keeling) Islands, to research and write the history of that principality in the Indian Ocean.
After completion, the manuscript was not published as the Commissioner felt that it differed from his own recollection of events during his rule.
Among other books by Souter are two histories of John Fairfax Limited: Company of Heralds (1981), which won the Foundation for Australian Literary Studies award;[3] and Heralds and Angels: the House of Fairfax 1841-1990 (1992), which won the Victorian Premier's Literary Award.
Souter was appointed a Member of the Order of Australia (AM) in 1988,[4] and raised to Officer level (AO) in 1995.