1943, he joined Antifascist association for Writers and Artists. The first congress of Communist Party of India was organized in Bombay on May 25th 1943. Simultaneously IPTA (Indian Peoples Theatre Association) and All India Progressive Writers’ Association held a conference, which was represented by Mitra from Bengal. In the month of July, 1943 he was nominated as the director in charge for IPTA’s Bengal zone theatre squad, along with Sudhi Pradhan as the secretary, and Hemanta Mukhopadhaya in charge of the song squad. In 1944 Nabanna was staged under the banner of IPTA, in Srirangam Mancha, jointly administered by Mitra and Bijon Bhattacharjee. Shambhu Mitra not only acted as Dayal Mondol in the play but was the director, set director, and music director of Nabanna.
Year 1947, he distanced himself from IPTA , a year before which he had produced for the association Muktodhara a play by Rabindranath Tagore. By this time Mitra had felt the need to work independently based on his theatrical aesthetics. He went on to form a theatre group named “Ashok Majumder O Somprodaye” with the help of Manoranjan Bhattacharjee, the members included, Ashok Majumder, Amar Ganguly, Mohammad Zakaria, Jalad Chattopadhaya, Rabin Bhattacharjee, Ritwik Ghatak and others. In 1948 this group staged Nabanna at Rangmahal but not under the banner of IPTA.
Bohurupee the theatre group was born in 1950, having Manoranjan Bhattacharjee as its President and Mitra as the director. The group’s first staged production was Ulukhagara and Cherataar . Bohurupee’s second production Bibhah (1951) was adopted from a Kabuki Play. Rabindranath’s Char Adhay staged at Srirangam in the same, by Bohurupee. Henrik Ibsen’s Enemy of the People was translated by Shanti Basu as Dasachakra, was Bohurupee’s next production directed by Mitra. In the year 1954 Mitra directed Rabindranath Thakur’s Raktakorobi (Red Orleanders) first staged at Railway Mansion Institute. Tripti Mitra directed Rabindranath Thakur’s Dakghar (Post Office) staged at New Empire in 1957, where Shambhu Mitra played the character of either Thakurda (grandfather) or Raj Kobirej (Medicine Man). Same year he was awarded with Grand Pix Award from Carlovy Film Festival for Jaagte Raho (1956). Honoured with Sangeet Natak Academy Award (1959), in the same year he was invited as an eminent thespian from India to U.S.S, Czechoslovakia, Yugoslavia, and Poland.
Bohurupee produced Ibsen’s A Doll’s House, Putul Khela, 1958, at Mahajati Sadan. Rabindranath Thakur’s Biswarjaan (Sacrifice), 1961, was first staged at Delhi’s IFAX Hall, under Bohurupee’s banner, directed by Mitra. Sophocles’ Oedipus Rex, translated, directed and acted by Mitra as Raja Oedipus (1964) was produced by Bohurupee at New Empire. He was invited to attend the Theatre Convention, America in the year 1965. Year next he was selected as the fellow of Sangeet Natak Academy. Bohurupee’s next production was Badal Sarkar’s Baki Itihaas (1967), directed by Mitra. Mitra resigned from Bohurupee in 1968 due to organizational squabble. He had the prophetic idea of establishing a National Theatre Auditorium; with the vision in mind he crafted an association “Bangla Natmancho Protistha Somiti”. The then government was unable to provide a construction site and enough land suitable for a theatre auditorium. He was honoured with PadmaBhushan on behalf of Government of India in the year 1970.
Bohurupee’s first theatre periodical in 1955 published Mitra’s “Raktakorobi Prosonge”. Other articles by Mitra published in the periodical were:
Bhejaler Aeitijhya 1957
Abhinoy O Konthoswaar 1958.
Manchosaajyar Bhumika (in pseudo name Atanu Lahiri), 1958.
Bhongir Sabolilota (adopted from Stanislavsky, written in pseudo name Nayanaranjan Roy), 1958.
Amader Akangsha O Amra, 1958.
Natya Sanskriti O Naboporjayer Proyojon, 1960.
Koekti Prosno, 1962.
Promiti Proshokto (in pseudo name Suranjan Chattopadhaya), 1962.
Moholar Proyojon Ki (in pseudo name Khanesh Prasad Dutta), 1962.
Nabo Natya Andalaan (in pseudo name Suranjan Chattopadhaya), 1962.
Kichu Purono Kotha, 1963.
Ekti Alochona, 1963.
Sophocleser Raja Oedipus, 1965.
Rajar Kothaye, 1965.
Brecht Prosonge, 1965.
Chaand Baniker Pala (First Part, in pseudo name Batuk), 1965.
Chaand Baniker Pala (Secon Part, in pseudo name Batuk), 1966.
Mitra’s active contribution as an actor, playwright, assistant director and director in the films commenced from the year 1945, some of which are:
Dharti Ke Lal (1945) directed by Kwaja Ahmad Abbas, playwright and assistant director Shambhu Mitra.
Acted in Abhinetri (1947) directed by Hemen Gupta.
Acted in Dhatri Debota (1949) directed by Kaliprasad Ghosh.
Acted in Aaborto (1950) directed by Biswakarma.
Acted in the English film Our India (1950) directed by Paul Jills.
Acted in Bodhoday (1951), along with wife Tripti Mitra directed by Niranjan Pal.
Acted in Bialliash-42 (1951) directed by Hemen Gupta.
Acted in Maharaj Nadakumar (1953), along with Tulsi Lahiri, Utpal Dutta and Bhanu Bandyopadhyay, directed by Biren Das.
Acted in Pathik (1953) along with Tripti Mitra, Tusi Lahiri, Kumar Roy, directed by Debaki Kumar Basu.
Acted in Bouthakuranir Haat (1953) directed by Naresh Mitra.
Acted in Maroner Pore (1954) directed by Satish Dasgupta.
Acted in Shibshakti (1954) directed by Ardhendu Chattopadhaya.
Ekdin Raatre storywriter, playwright and co director with Amit Moitra. This was the first and the last bangle film ever produced under the Raj Kapoor (R.K) Banner. The much appreciated Hindi version was Jaagte Raho (1956), Raj Kapoor as the protagonist.
Acted in Durlobh Jonom (1955) directed by Prafulla Chakraborty.
Directed along with Amit Mitra Shubho Bibhaho (1959), actors in the film were Tripti Mitra, Chobi Biswas, Kuruna Bandyopadhaya.
Acted in Manik (1961), along with Tripti Mitra, Amar Ganguly, Chobi Biswas, Pahari Sanyal, Gangapada Basu, Kumar Roy, based on a novel by Charles Dickens, directed by Bijlibaran Sen.
Acted in Surjasnan (1962), directed by Ajay Kumar.