[clarification needed][3] After joining MC College Nirmalendu got involved in the activities of the Communist Party.
Song became an instrument for awakening the masses against the oppression of the British, and Nirmalendu engaged himself fully in that pursuit.
He got acquainted with Hemanga Biswas, another son of the soil of Sylhet, who was a proficient musician and politically aligned to the Communist Party.
During 1953 Anil Kumar Chanda, the then Deputy Minister for External Affairs, invited Nirmalendu and his brother Nirendu Chowdhury to join an Indian Cultural Delegation to Eastern European countries as a preparatory program for Pandit Jawahar Lal Nehru's visit to Soviet Union and other countries.
Dancer Sitara Devi, vocalist Lalita S Ubhayakar, Rabidra Sangeet artist Dwijen Mukherjee, Tabalia andit Shanta Prasad were among others in the delegation.
[4] In 1955 Nirmalendu performed in the grand Bolshoi Theater in Moscow in the presence of Nikita Khrushchev, and later won a gold medal singing at an international folk song convention in Warsaw.
His performances in Warsaw, Sofia, Prague, Belgrade and Moscow were received by the people with great accolade making Indian folk songs popular to outside world.
[1] He visited many countries including Soviet Union, Yugoslavia, Poland, Hungary, Romania, Czechoslovakia, Bulgaria, Australia, New Zealand, China, United Kingdom, France, Germany, Holland, Finland, USA, Canada, and Japan.
[1] Nirmalendu helped in revitalization and propagation of various forms of folk songs of Bengal, Assam and Tripura.
[5] Some examples are: Nirmalendu was involved with Indian People's Theatre Association (IPTA) from an early age.
Nirmalendu acted in theatrical plays along with Utpal Dutta in Aungar (অঙ্গার), Pherari Phauj (ফেরারী ফৌজ) and Titas Ekti Nodir Naam"(তিতাস একটি নদীর নাম).
"[6]"As the lights dimmed in the grand Bolshoi Theatre in Moscow, and the Russian sopranos’ voices soared divinely, the young Vilayat Khan started worrying about how the Indian performers could match this beauty.
He announced, ‘I want you to hear this folk tune which I had heard Nirmalendu Chowdhury sing many many years ago.
His son Utpalendu Choudhury carried on the task of propagating and popularizing folk music in line with his father until he died on 6 February 2011.