Majumdar started his research on ancient India. After extensive travels to Southeast Asia and research, he wrote detailed histories of Champa (1927), Suvarnadvipa (1938) and Kambuja Desa (1944). On the initiative of Bharatiya Vidya Bhavan, he took up the mantle of editing a multi-volume tome on Indian history. Starting in 1951, he toiled for twenty-six long years to describe the history of the Indian people from the Vedic Period until the Independence of India in eleven volumes. In 1955, Majumdar established the College of Indology of Nagpur University and joined as Principal. In 1958–59, he taught Indian history in the University of Chicago and University of Pennsylvania. He was also the president of the Asiatic Society (1966–68) and the Bangiya Sahitya Parishad (1968–69), and also the Sheriff of Calcutta (1967–68).