Sir John Angus Nimmo was born at Ballarat on 15 January 1909 to John James and Grace (née Mann) Nimmo. He was the eldest of four brothers and moved to Melbourne with his family when he was ten years old. John lived in Melbourne and studied law at Melbourne University. By 1933, he had graduated and was practicing as a barrister at the Victorian Bar. John married Teanie Rose Galloway in 1935.

John Nimmo was rejected for active service due to blindness in his left eye (caused by an air rifle incident in childhood). However, he volunteered for the Australian Red Cross as a field force officer (‘searcher’), establishing the fate of soldiers missing in action in the Middle East and Papua New Guinea. He also travelled to Europe as a representative of the Australian Red Cross attached to the Prisoner Recovery Unit.

After the war, Nimmo returned to Melbourne to continue practicing law. Throughout his career he held many significant positions, including Justice of the Supreme Court of the Northern Territory (1969-1974) and Chief Justice of Fiji (1972-1974). He was also appointed a Knight Bachelor in 1972. In February 1977 he was appointed Judge of the Federal Court of Australia, a role he held until 1980 before moving back to Victoria.

He and Teanie had one son. By 1980, Sir John Nimmo had retired and was living at Mount Eliza, Victoria. He died on 7 July 1997.