 He contested Bakharganj North East Rural constituency for a seat in the Bengal legislative assembly and defeated Saral Kumar Dutta, the president of the district committee of the Indian National Congress (INC) and nephew of the Swadeshi leader, Ashwini Kumar Dutta.Mandal was considerably influenced around this time by both Subhas Chandra Bose and Sarat Chandra Bose.When the former was expelled from the INC in 1940, Mandal became involved with the Muslim League (ML), which was the only other significant national party, and became a minister in the cabinet of the ML chief minister, Huseyn Shaheed Suhrawardy.