Islam served as a Professor of History at the University of Dhaka. He gave up his day job five years before the formal date of retirement, to make time for Banglapedia, in 2000.
A corresponding fellow of the Royal Historical Society, Islam was a Senior Commonwealth Staff Fellow at the University of London (1978–79), a Senior Fulbright Scholar at Urbana Champaigne (1990–91), and a British Academy Visiting Professor (2004).
In 2002, 10 volumes of Banglapedia, published by Asiatic Society, came out in his editorship. In 1991, 3 volumes of the History of Bangladesh (political, economic and socio-cultural), published by Asiatic Society, came out in his editorship. For the Society, he is working on the Children’s Banglapedia and the Cultural Survey of Bangladesh. He also is in charge of the National Online Biography project of the Society and the Banglapedia Trust.
While at his 34-year-long stint at the University, he wrote major seminal works like Permanent Settlement in Bengal (1978), The Bengal Land Tenure (1990) and the Rural History of Bangladesh (1990). He also edited the 4 volume Bangladesh District Record Survey.
- Khan, Mubin S (2006-01-01). "Professor Sirajul Islam: Making history". New Age New Year Special 2006. The New Age. Retrieved 2007-06-07.
- "Sirajul Islam (Dhaka University)". International Directory of South Asia Scholars (IDSAS). Columbia University. 2004-04-21. Archived from the original on September 11, 2007. Retrieved 2007-07-23.