Jenkin was born in January 1938 at Cwmgiedd, Upper Swansea Valley. Educated at Maesydderwen Grammar School, University College London & University of Michigan, Ann Arbor. He served as a member of HM Foreign & Diplomatic Service between 1960 and 1995, serving in Foreign and Cabinet Offices and abroad. Overseas postings included Pretoria/Capetown, Saigon, Washington DC, Tokyo, Athens and Paris(OECD).