The Tattwabodhinī Sabhā ("Truth Propagating/Searching Society") was a group started in Calcutta on 6 October 1839 as a splinter group of the Brahmo Samaj, reformers of Hinduism and Indian Society. The founding member was Debendranath Tagore, previously of the Brahmo Samaj, eldest son of influential entrepreneur Dwarkanath Tagore, and eventually father to renowned polymath Rabindranath Tagore. In 1859, the Tattwabodhinī Sabhā were dissolved back into the Brāhmo Samāj by Debendranath Tagore.
On 6 October 1839 Debendranath Tagore established Tattvaranjini Sabha which was shortly thereafter renamed the Tattwabodhini (Truth-seekers) Sabha. Initially confined to immediate members of the Tagore family, in 2 years it mustered over 500 members. In 1840 Debendranath published a Bangla translation of Katha Upanishad. A modern researcher describes the Sabha's philosophy as modern middle-class (bourgeois) Vedanta. Among its first members were the "two giants of Hindu reformation and Bengal Renaissance, Akshay Kumar Datta "who in 1839 emerged from the life of an anonymous squalor-beset individual" and Ishwar Chandra Vidyasagar the "indigenous modernizer".
On 7th Pous 1765 Shaka (1843) Debendranath Tagore and twenty other Tattwabodhini stalwarts were formally invited by Pt. Vidyabagish into the Trust of Brahmo Sabha. The Pous Mela at Santiniketan starts on this day. From this day forth, the Tattwabodhini Sabha dedicated itself to promoting Ram Mohan Roy's creed. The other Brahmins who swore the First Covenant of Brahmoism are:-
In Nov 1855 the Rev. Charles Dall (a Unitarian minister of Boston) arrived in Calcutta to start his mission and immediately established contact with Debendranath and other Brahmos. Debendranath's suspicion of foreigners alienated Dall and in 1857, Debendranath Tagore barred the entry of the Reverend from the Sabha premises for preaching the name of Christ who some people worship as God within. Debendranath then proceeded on spiritual retreat to Simla. Dall, immediately formed a counter group "The friends of Rammmohun Roy Society" and then got admitted a protégé to Sabha. The presence of Dall's protégé Keshub Chandra Sen (a non-Brahmin) into the Calcutta Brahmo Sabha in 1857 while Debendranath was away in Simla caused considerable stress in the movement, with many long time Tattvabodhini Brahmin members publicly leaving the Brahmo Sabha and institutions due to his high-handed ways. In September 1858, Debendranath returned to Calcutta to resolve the simmering disputes. but his conservative mien did not allow him to take decisive steps. He proceeded on a sea voyage to Ceylon accompanied by Sen and his 2nd son Satyendranath (a firm admirer of Mr Sen) but no concord was achieved. In 1859, the venerable and beloved Secretary of the Tattwabodhini Sabha Ishwar Chandra Vidyasagar resigned from the Brahmo Sabha in the face of Debendranath's vacillation. A meeting of the Tatwabodhini was promptly summoned with Debendranath resigning from the group he had founded. His third son Hemendranath Tagore then a boy barely 15 years in age, and the favorite pupil of Vidyasgar, was commonly acclaimed as Debendranath's successor to head the Tattwabodhini. In the course of time he would become known as the MahaAcharya (or Great Teacher).