Alexander Roland Campbell Johnstone was born on 5 January 1912 at Willoughby, New South Wales to Percival Campbell Johnstone and Alleyne Muriel Jackson. He had two siblings, Jessie M. born in 1909 and Gloria M. born in 1917. In 1933 Johnstone was living in Yass, New South Wales and working as an accounting clerk.

Johnstone married Marguerite “Peggy” Macbean at Yass, New South Wales on 7 June 1940 and enlisted in the Second Australian Imperial Force one week later on 14 June 1940. He was initially assigned to the 2/15 Field Regiment but transferred to the audit staff, Command Pay Office around October 1941. He was incarcerated as a prisoner of war in Changi, Jinsen and Keijo camps between 15 February 1942 and 15 August 1945. Johnstone was discharged on 7 December 1945.

After his return to Australia, Johnstone worked as an accountant and lived in Cairns, Queensland and Burwood, New South Wales before settling in Mosman, New South Wales. He and Peg had two daughters, Suzette and Janette. Alexander Roland Campbell Johnstone later moved to Narrabundah, Canberra, Australian Capital Territory, and died in Canberra on 24 May 1967 at the age of 56. His remains are held at Norwood Park Crematorium, Mitchell, Australian Capital Territory.