John was born and went to school in Oxford. He read Classics at Exeter College, Oxford. His career has been in IT from 1962 initially with the Ford Motor Company where he did pioneering work on computer systems in finance and manufacturing, Plessey (where he was Head of Management Services) and British Leyland (from the early 1970s). In 1987, he led an employee buyout of ISTEL Ltd, which he had established as a subsidiary of British Leyland. In 1989, the company was acquired by AT&T. He was the Executive Chairman of AT&T ISTEL and an officer of AT&T until April 1993.
In November 1993, he joined RM (a British educational computing company) as a non-executive director and in October 1994 became Chairman. He has been a non-executive director of a number of other companies including Halifax plc and Synstar plc (of which he is also Chairman).
John was President of the British Computer Society (1993–4) and the Computing Services and Software Association (1995–6). He was President of the Institute for the Management of Information Systems (IMIS), a UK professional association. He has been a member of the Council of University of Warwick, Chairman of the Advisory Board, and an honorary visiting professor at the Warwick Business School and Warwick Manufacturing Group. He was Pro-Chancellor and Chairman of the Council at the University of Warwick from 2002 to 2011.
In the Queen’s Birthday Honours 1998 Leighfield was appointed as a Commander of the Most Excellent Order of the British Empire. In 2006 Leighfield was awarded the Mountbatten Medal which is awarded annually for an outstanding contribution to the promotion of electronics or information technology and their application.
Currently he is Chairman of Governors of the WMG Academy for Young Engineers (a UTC) and a member of the Development Committee of the Bodleian Library, Oxford.
He is a founder member and Past Master of the Worshipful Company of Information Technologists.
He has an MA from Oxford, and Honorary Doctorates from the University of Central England in Birmingham (DUniv), from De Montford University (DTech), from Wolverhampton University (DTech) and from the University of Warwick (DLL). He is a Fellow of the RSA, RGS, CMI, IET and BCS.