Hoskyns was born in August 1927, the son of Lt-Colonel Chandos Benedict Arden Hoskyns and Joyce Austin Hoskyns. He was educated at Winchester College before serving as a regular solider in the Rifle Brigade (1945-57). He started his business career at IBM United Kingdom Ltd (1957-64), before founding John Hoskyns & Co. Ltd, which was later part of Hoskyns Group Ltd (where he was Chairman and Managing Director, 1964-75). He acted as a part-time Policy Adviser to Margaret Thatcher MP (then Leader of the Opposition Conservative Party) from 1975-77, and was then a full-time adviser to Mrs Thatcher and the Shadow Cabinet, 1977-79. His best known contribution of this period was the production of the "Stepping Stones" report of November 1977. He was subsequently appointed by Mrs Thatcher to be Head of her Prime Minister’s Policy Unit, where he served between May 1979 and April 1982. He was subsequently Director-General of the Institute of Directors, 1984-89, and served on the boards of a number of public companies. Hoskyns was knighted in 1982. He published a memoir, "Just in time, inside the Thatcher revolution" in 2000. He died in October 2014.