John Gridley was born on 28 May 1904, the only son of William Joseph Gridley and Mary Ellen (née Michell). He was educated at Queen’s College, Taunton (and was granted an honorary degree by London University in 1967). In 1933 he married Joan Marion, elder daughter of Sir Herbert Merrett, having two sons; he and his wife were briefly divorced in 1950, but remarried in 1951.

John Gridley spent his pre-war career in South Wales shipping and coal businesses, and from about 1928 worked for the Cardiff coal company Gueret Llewellyn and Merrett (later bought by Powell Duffryn), initially in Spain. In the late 1930's Gridley worked with his employer and father-in-law Herbert Merrett, travelling extensively in Europe and South America.

During the early years of the war he continued to work in the coal industry, and was involved in the issues of wartime coal supplies. He was then appointed temporarily to the Coal Division of the North African Economic Board [NAEB] in Algiers in 1943, returning to Algiers in December of that year to become the British Joint Chairman of the North African Joint Economic Mission, remaining in this post until August 1944. He was then appointed as Economic Adviser to [Alfred] Duff Cooper, the British Ambassador to France, in October 1944. His main task was to restore supplies of coal and steel to France, but he was also Economic Adviser at the Supreme Headquarters Allied Expeditionary Force (SHAEF) and served on the Inter-Allied Railway Commission, eventually leaving Paris in mid-1945.

After the war, Gridley became Chairman of the European Coal Organisation, (1945-46), and was a founding member and Marketing Director of the National Coal Board, (1946-48). He was Chairman of Mobil Oil Company Limited, (1948-68) and President of the Institute of Petroleum, (1962-1964), also serving as Director of Powell Duffryn Limited and other companies. He was awarded the CBE in 1945.

Gridley died on 25 November 1968.