He was born in Calcutta to Basanta Kumar De, esq., an officer of the Bengal Nagpur Railway and Pramila Dé [nee Gupta]. His paternal grandfather was Brajendranath De, esq. ICS, who was a well known historian of medieval India. His maternal grand-uncle was Amrita Lal Gupta, a well known Brahmo preacher.
He studied at Presidency College, Calcutta and holds an M.A. and D.Phil. in British Indian Constitutional History from St Catherine's Society, Oxford, and Nuffield College, Oxford. While in Oxford he was awarded the Curzon Memorial Essay Prize. He was Senior Professor of Social and Economic History and Post-Graduate Programme Director of the Indian Institute of Management, Calcutta. He was the First-Director of the Centre for Studies in Social Sciences, Calcutta (founded in 1973), where he was a Professor from 1973-93, and also of the Maulana Abul Kalam Azad Institute of Asian Studies, Calcutta (founded in 1993), where he was also a Maulana Azad Fellow and of whose Society he is now a member. He was conferred an Honorary Doctor of Letters, Honoris Causa by the North Bengal University in 2000.
He has variously taught as Visiting Professor, Visiting Associate Professor and Tutor and held Directeurships at universities, institutes and colleges at Oxford, Duke, Simla, Paris, Milan, Sydney, Tashkent and the UNU.
He was State Editor of the West Bengal District Gazetteers. He was elected the General President of the Indian History Congress, Dharwar Session, 1988 (of which he was a General Secretary from 1974-1976). Presently, he is Chairman of the West Bengal Heritage Commission (of which was until recently a member), the Advisory Board of the Directorate of Archeology, Government of West Bengal, and the West Bengal State Archives. He was also Chairman of the Gurusaday Dutt Folk Art Society, Calcutta (on whose Governing Body he was a family nominee for several years). He was also the President of the Oxford India Majlis, of which he was the General Secretary as well. Presently, he is the Vice Chairman of the Centre for Archeology and Training, Eastern India, and is also a Vice President of the Asiatic Society, Calcutta.
He was and is a member of numerous organisations, including the Executive Council (Karma Samiti) of Visva-Bharati University, Santiniketan, Indian Council of Historical Research, New Delhi, (of which he was a member from its inception in 1972 to 1978, and then again from 2004 until the present), the general council of the Indian Council for Cultural Relations, New Delhi, numerous committees of the Indian Council for Social Science Research, New Delhi, the Executive Councils of the Indian Statistical Institute, Calcutta, Centre for Development Studies, Trivandrum, A.N.Sinha Institute of Social Sciences, Patna, the Board of Trustees of the Victoria Memorial Hall, Calcutta, the governing body of the Indian Museum, Calcutta, West Bengal Commission for the Planning of Higher Education, Heritage Buildings' Committee and the Road Renaming Committee of the Calcutta Municipal Corporation.
Since the 1960s he has been intensely involved in the secular and Communist Movement in India. Through the 1970s, especially after the founding of the Centre for Studies in Social Sciences in Calcutta, he was criticised by right-wing and communal historians for his involvement in Marxist historiography. He was known both for his rejection of the historiography produced by the Bharatiya Vidya Bhawan Series, as well as his severe condemnation of the Emergency between 1975 and 1977. The communalised forces' attacks on the Congress and the left intensified and then peaked in the period between 1977-1980 when the first non-Congress government was formed at the Centre. Under the orders of the then union cabinet, he was once again abused by right-wing historians in the Jansatta, the mouthpiece of the Jan Sangh, which had not criticised the imposition of the Emergency. Through the 1980s, he remained vocal in his criticism of the communal forces, in his articles and lectures, especially those delivered at the annual Indian History Congress sessions. In the 1990s too, after the founding of the Maulana Abul Kalam Azad Institute of Asian Studies in Calcutta, he was bitterly criticised in certain quarters, mainly in Delhi, for his steadfast support for leftwing, secular and progressive history writing in India and its application to Area Studies.
Most recently, in 2004, he was appointed to a national level committee appointed by the ruling UPA Government to review the textbooks published by the NCERT under the NDA regime. The committee in its report recommended the removal of the history textbooks, mainly on the grounds of being totally biased towards the historiography produced by communal historians and also because they were full of glaring factual and interpretative errors. The newspaper reports, on the findings of the committee, were predictably polarised. The first group of newspapers, consisting of leftwing and centrist newspapers, were supportive of the recommendations of the committee., A second group of newspapers supported the efforts of the secular historians to detoxify the previous regimes history textbooks, but suggested that the NCERT history textbooks could be reviewed periodically in order to make them relevant to the time they are being taught in. A third group of newspapers, both published from India and the west, have been either very sceptical or openly hostile to him and other committee members for the views they expressed in the report., This issue remains very relevant and a vexious one in contemporary Indian politics.