David Forrest served with the Australian army, in New Guinea, during World War II and then worked in the banking industry until 1964. He later undertook tertiary study at the University of Queensland and the Australian National University, gaining a degree and Ph.D in history. At the completion of his studies Forrest became an academic and taught history at the Riverina College of Advanced Education.

Writing under his birth name, David Denholm, Forrest was also the author of a pamphlet on land use in New South Wales and of The Colonial Australians (Harmondsworth, Victoria : Penguin , 1979).