Medley was the eldest of seven children of Dudley Julius Medley and his wife, Isabel Alice, nee Gibbs. The father was a tutor at Keble College who went on to become a professor of history at the University of Glasgow. Medley suffered from osteomyelitis as a child and read voraciously. In his time at Winchester College he won successive prizes in English and classics, acted in a Shakespearian group, edited the Wykehamist, was joint school captain and won a scholarship to New College, Oxford. Greatly influenced by the classicist Gilbert Murray, Medley took a B.A. with first class honours in 1914 before enlisting in the British Army.

Medley survived the First World War and joined the family firm of Antony Gibbs and Sons which transferred him to branch offices in Adelaide and Sydney from 1920. He left the firm in 1930 and made a success of running Tudor House, an Anglican school at Moss Vale. In 1938 he was appointed Vice-Chancellor of the University of Melbourne as a compromise candidate when agreement could not be reached on the appointment of Douglas Copeland. He surprised with his liberalism and strengthened the position of professors vis-a-vis the university council.

Medley developed a high profile as a public speaker and active participant in public life. He gave a series of talks for the Australian Broadcasting Commission in 1940 to raise public morale and was in the Educationsal Reform Association and President of the Australian Council for Educational Research. Medley was chairman of the Australian Services Education Council. He chaired the Australian Vice-Chancellor's Committee for a decade and was a key adviser to government on higher education policy. In 1946-51 Medley was deputy-chairman of the interim council of the Australian National University.

Serle comments in the Australian Dictionary of Biography that his 'occasional verse was privately published as Stolne and Surreptitious Verses (1952), followed by An Australian Alphabet (1953). In his last years he enjoyed making colloquial translations of Horace and Catullus. His most astounding activity was to write for the Saturday Age nearly 500 weekly essays, about anything and everything, which won a devoted public. He constantly defended the young and was determined not to become an angry old man.'

(Source: Geoffrey Serle, 'Medley, Sir John Dudley Gibbs (Jack) (1891 - 1962)', Australian Dictionary of Biography, Volume 15, MUP, 2000, pp 344-346.)