In 1944, several old theatrical conventions were broken when the play Nabanna written by Bijon Bhattacharya and co-directed by Sombhu Mitra for IPTA was staged.
In 1948, Sombhu Mitra formed a new theatre group, Bohurupee in Kolkata, which ushered in the group-theatre movement in West Bengal.
In December 1950, the Bohurupee presented three plays in the New Empire theatre – Tulsi Lahiri's Pathik and Chenda Tar and Sombhu Mitra's own creation, Ulukhagra.
In 1954, Rabindranath Tagore's Rakta Karabi was staged by the Bohurupee, followed by his Bisarjan, Raja and Char Adhyay.
Henrik Ibsen's Putul Khela (Doll's House), Dashachakra (An Enemy of the People) and Sophocles' Raja Oidipaus (Oedipus Rex) are notable amongst them.
He has also acted in The Life of Galileo by Bertolt Brecht directed by Fritz Bennewitz in the title role.