Peter Allen Ryan was born on 4 September 1923, and educated at Malvern Grammar School. He joined the Victorian Crown Law Department but left in 1941 at the age of 18 to enlist in the Army. For eighteen months he worked on special intelligence work in PNG behind Japanese lines, winning the Military Medal in 1943 and being mentioned in dispatches.
When he returned to Australia he was posted to Victoria Barracks in Melbourne. In 1944-45 he was an officer in the Army's Directorate of Research and Civil Affairs under Colonel Alf Conlon, serving both in Melbourne and at the Land Headquarters School of Civil Affairs – ASOPA’s progenitor - at Duntroon.
In 1946-48, Peter was at the University of Melbourne, graduating with an honours degree in History. While studying Australian history he was taught by Manning Clark. In time, Peter was to become Clark's publisher of the six volumes of a History of Australia. In 1993 he caused a major controversy by publishing a long essay in Quadrant criticising Clark's character and his writings.
From 1958-62, Peter was Public Relations Manager of Imperial Chemical Industries and in 1962 became Director of Melbourne University Press, where he was to remain until his retirement in 1988. Works published during his directorship of MUP included the first twelve volumes of the Australian Dictionary of Biography (to which Ryan was also a contributor), Insects of Australia and Norman Lindsay's Micomicana and books by such well-known authors as Manning Clark, Macfarlane Burnet, Paul Hasluck and AD Hope. Ryan was also pivotal in establishing MUP's high quality publishing subsidiary, Miegunyah Press.
Later Peter held a number of executive positions, including member of the Solicitors Disciplinary Tribunal (1985-88); Executive Officer for the Council of Legal Education (1988-2003); Administrative Officer, the Council of Law Reporting in Victoria; and Secretary of the Victorian Board of Examiners for Barristers and Solicitors. He retired from the latter two appointments in 2003.
In addition to numerous press articles and book reviews, Peter wrote several books including Fear Drive My Feet (1959), Redmond Barry (1972), William Macmahon Ball: A Memoir (1990), Black Bonanza: A Landslide of Gold (1991), Chance Encounters: AD Hope (1992), Lines of Fire: Manning Clark and Other Writings (1997) and Brief Lives (2004).