Gavin Long, a journalist and historian who wrote three volumes of the official history of Australia in the Second World War, was born at Foster, Victoria, on 31 May 1901. He was educated at Trinity Grammar School and later at All Saints College in Bathurst, New South Wales. He received his tertiary education at the University of Sydney and became a teacher at the King's School, Parramatta. In 1924 he left teaching to become a jackeroo.

The following year, 1925, Long travelled to England where he worked at Australia House in the Migration and Settlement Office. In September 1925 he married Jocelyn Britten, an Australian who was holidaying in England, and returned to Australia in 1926. Having had some contributions to newspapers and journals published, he sought work as a journalist and was employed by the Daily Guardian in Sydney before moving to the Melbourne Argus. In 1928 he was promoted to general reporter for the Argus and just over a year later he was promoted again, to senior reporter, before the depression forced a demotion to his former status. In 1931 he accepted an appointment as a senior reporter with the Sydney Morning Herald.

In 1938, having worked as Chief Cable Sub-editor on the Herald, he was posted to that paper's London office and, when the Second World War began, he became a war correspondent with the British Expeditionary Force in France. After the evacuation, he reported on the Royal Navy and, in November 1940, was sent to Egypt to cover Australian operations in the Mediterranean. He was recalled to Australia in mid-1941.

Long was appointed general editor of the Official History of Australia in the Second World War in March 1943. Based at the Australian War Memorial in Canberra, he drafted a volume on the Syrian campaign and recruited staff and authors. At the same time he made several visits to Australian troops at the front, interviewing participants in various campaigns and amassing many volumes of notebooks.

At its completion, the official history series comprised 22 volumes, of which Long wrote three. It was the largest historical project undertaken in Australia and Long's first two volumes were published in 1952 and 1953 respectively. The last of the series was published in 1977.

Long retired in 1963, the same year that his final volume, The final campaigns, was published. Between 1963 and 1965, Long worked as a research fellow with the Australian Dictionary of Biography. He had been a board member of the Australian War Memorial since 1943 and remained in this post until 1968. In addition he was involved in the production of Australia's official Style manual and was a regular contributor to the Canberra Times. Long also produced a concise volume to accompany the official history series, The six years war, which was published in 1973. He died in Canberra of lung cancer on 10 October 1968.