From 1942 to 1945 during the Second World War, Asa Briggs served in the Intelligence Corps and worked at the British wartime codebreaking station, Bletchley Park. He was a member of “the Watch” in Hut 6, the section deciphering Enigma machine messages from the German Army and Luftwaffe. This posting had arisen because at college Briggs had played chess with Cambridge mathematician Howard Smith (who was to become the Director General of MI5 in 1979) and Smith had written to the head of Hut 6, Gordon Welchman, who was also a Cambridge mathematician, recommending Briggs to him.After the war, he was elected a Fellow of Worcester College, Oxford (1945–55), and was subsequently appointed University Reader in Recent Social and Economic History (1950–55). Whilst a young Fellow, Briggs proofread Winston Churchill’s A History of the English-Speaking Peoples. He was later Faculty Fellow of Nuffield College (1953–55) and a member of the Institute for Advanced Study, Princeton, New Jersey, United States (1953–54). From 1955 until 1961 he was Professor of Modern History at Leeds University and between 1961 and 1976 he was Professor of History at Sussex University, while also serving as Dean of the School of Social Studies (1961–65), Pro Vice-Chancellor (1961–67) and Vice-Chancellor (1967–76). On 4 June 2008 the University of Sussex Arts A1 and A2 lecture theatres, designed by Basil Spence, were renamed in his honour. In 1976 Asa Briggs returned to Oxford to become Provost of Worcester College, retiring from the post in 1991.

Asa Briggs was Chancellor of the Open University (1978–94) and in May 1979 was awarded an honorary degree as Doctor of the University. He had been an Honorary Fellow of Sidney Sussex College, Cambridge, from 1968, of Worcester College, Oxford, from 1969, and of St Catharine’s College, Cambridge, from 1977. He also held a visiting appointment at the Gannett Center for Media Studies at Columbia University in the late 1980s and again at the renamed Freedom Forum Media Studies Center at Columbia in 1995–96. Announced in the 1976 Birthday Honours, he was created a life peer as Baron Briggs, of Lewes in the County of East Sussex on 19 July 1976. Between 1961 and 1995, Briggs wrote a five-volume text on the history of broadcasting in the UK from 1922 to 1974 — essentially, the history of the BBC, who commissioned the work. Briggs’ other works ranged from an account of the period that Karl Marx spent in London to the corporate history of British retailer Marks and Spencer. In 1987, Lord Briggs was invited to be President of the Brontë Society, a literary society established in 1893 in Haworth, near Keighley, Yorkshire. He presided over the Society’s centenary celebrations in 1993 and continued as President until he retired from the position in 1996. He was also President of the William Morris Society from 1978 to 1991 and President of the Victorian Society (UK) from 1986 until his death. He died at home in Lewes at the age of 94 on 15 March 2016.