In 1929, Graham married Winifred Emily Ware (1907-1990), with whom he had a son. They divorced in 1950 and he married Constance Mary Greey, with whom he had two daughters and a son.
For 1940-41, he was awarded a Guggenheim Fellowship that resulted in Graham's first major book that showed his shift of research interests to British naval history: Sea Power and British North America, 1783- 1820. Toward the end of 1941, he joined the Canadian Army, but quickly shifted to the Royal Canadian Naval Volunteer Reserve and was appointed an instructor lieutenant commander to teach entering officers at Royal Roads Military College. While teaching there, Graham was able to get first-hand experience of the war at sea, by spending time during academic breaks on board Canadian destroyers in the Atlantic and in torpedo boats at Dover. Following the allied landings in northern France in 1944, Graham was returned to the Canadian Army as a major, and served with the historical section of the Canadian Army Overseas in London.
Graham's military assignment to London was the event that led him to stay in Britain for the remainder of his career. After demobilization, he was appointed lecturer in history at Birkbeck College, London, and in 1949 was elected to succeed Professor Vincent Harlow as Rhodes Professor of Imperial History at King's College London.
Gerald Graham served as Rhodes Professor for 29-years until his retirement at the age of 67 in 1970, when he was appointed professor emeritus. While in that academic post, Graham specialized in teaching the history of the British Empire in the period 1880-1932 and in British colonial history. He traveled and lectured widely through the Commonwealth.
In addition to his teaching, he worked closely with the Royal Commonwealth Society, to which he had initially been elected in 1928, later becoming a Life Fellow and Vice-President. He was a member of its Library Committee from 1948-1955, its Imperial Studies Committee in 1952-57, and chairman of its Academic Committee, which awarded the Walter Frewen Lord Prize for the best postgraduate essay in imperial history. In addition, revived the Society's monograph series, Imperial Studies, and he edited volumes XXII (1961) through XXIX (1970) of the series. Similarly in working with the Oxford University Press, Graham served as general editor of its West African History series, most of which became the standard works on this field.
In 1963-64, Queen's University, Belfast honoured Graham by inviting him to deliver the Wiles Lectures, which were published the next year by Cambridge University Press as The Politics of Naval Supremacy. In 1967, Graham delivered the Reid Lectures at Acadia University, which were published as Tides of Empire: Discursions on the Expansion of Britain Overseas]].
Immediately after Graham's retirement in London, he returned to Canada for two years as to serve as visiting professor of military and strategic studies at the University of Western Ontario in 1970-1972. After this appointment, Graham returned to his permanent home in England at St Leonards-on-Sea, where he died at the age of 85 in 1988.
John Flint, 'Graham, Gerald Sandford (1903-1988)' in Oxford Dictionary of National Biography (2006).