Mitra joined the Indian [National Congress]. He founded the Swaraj Sevak Sangha and was attached with HooghlyVidya Mandir which was headed by Bhupati Majumder, one of the Jugantar Leaders in 1922. He organised a Socialist conference in Kolkata in the presidency of Jawaharlal Nehru. After the suspension of Non-cooperation movement Mitra shifted to the extremist movement in the struggle for Independence. He was charged with Shankharitola Murder Case and arrested in 1923.