In 1828 Ram Mohun founded the Brahmo Sabha, which became famous as Brahmo Samaj in 1830. The Samaj laid emphasis on the worship of one omnipresent God. In the weekly meetings of the Samaj, the Vedic hymns were first recited in Sanskrit and later the Bengali version of the hymns was also read on every Saturday evenings. In these meetings about 50-60 persons participated. His main aim in founding the Samaj was to solve the problem of ordinary English educated families of Bengal, which were greatly disturbed by the propaganda of Christian missionaries. The Christian missionaries vehemently criticized doctrines and practices of Hinduism. Ram Mohun accepted only those doctrines, which were common to all the three religions namely Hinduism, Islam and Christianity. The Christian missionaries did not support the Brahmo Samaj, as their aim in cooperating with Ram Mohun was to spread Christianity. Brahmo Samaj laid emphasis on the worship of one formless omnipresent God. In the worship only excerpts from the Vedas and the Upanishads were recited. Ram Mohun never claimed that he had founded a new religion different from Hinduism. Probably he started the practice of weekly prayer meetings as a result of his contact with the Christian missionaries.

In founding Brahmo Samaj the aim of Ram Mohun was to purify Hinduism and to preach the worship of one God. The Samaj was based on those teachings of the Vedas and the Upanishads and also those of other religions, which had some rational basis.

The Brahmo Samaj has played a significant role in the renaissance of India, and the roots of much of the modern thinking in India can be traced back to the Brahmo movement. Rabindranath Tagore, the Nobel Laureate, was one of the luminaries of the Brahmo Samaj.

The movement was started on 20th August 1828 by Raja Rammohun Roy and his friends (Brajosundar Mitra and others) when they opened a place for public worship, Brahma Sabha on Chitpore Road Kolkata, India. It was publicly inaugurated on 11th Magh or 23rd January 1830. The former date is celebrated as Bhadrotsab and the latter as Maghotsab.

Raja Ram Mohan Roy found responsive echo in his heart towards Missionary attacks on idolatry. He found studies of the Upanishads as very rewarding. He was as much impressed by the monotheistic doctrine of the Upanishads. He began to consider reform of Hinduism by abolishing idolatry and establishing in its place the principle of `one true god`. The orthodox section of Brahmins developed a hostile attitude towards his preaching. In 1820 he published a book `The Percepts of Jesus, the Guide to Peace and Happiness`.

Deserted by the Orthodoxy he found his own sect of Unitarianism, along with the Baptist missionary William Adam. Hindus considered it to be a Christian sect. Meetings of the Samaj were held every Saturday evenings. These meetings started with recital of the Vedas in a side room, screened from the view of the people attending worship, where non-Brahmins were not admitted.

Though the procedure has been oriented on lines of Christian Church practices, the Primary belief of this Brahmo Samaj were not different from the Upanishads. English educated Hindus found an easy outlet in Brahmo Samaj from their divided loyalties between Church and Temple. As there was no idol to be worshipped, the place of worship was called church and not temple. But Saturday prayers and preaching were modeled on the Rig veda and Upanishads. This was sort of a worship of Nirguna Brahman-the one True Attribute less God.

The Orthodox Hindus were, however, incensed at this open revolt against the Hindu practices and rituals. They felt their religion was in danger with the founding of this new Church. The fundamental principles of the Brahmo Samaj, founded by Raja Ram Mohan Roy in 1828 are:
1. There is only one God, who is the creator, and the saviour of this world. He is spirit, infinite in power, wisdom, love, justice and holiness, omnipresent, eternal and blissful.

2. The human soul is immortal and capable of infinite progress, and is responsible to God for its doings.

3. Man`s happiness in this and the next world consists in worshipping God in spirit and in truth.

4. Loving God, holding communion with Him, and carrying out His will in all the concerns of life, constitute true worship.

5. No created object is to be worshipped as God, and God alone is to be considered as infallible.

But the worship of one omnipresent formless god soon excited the hostility of the orthodox citizens of Calcutta, who started a rival organization named the Dharma Sabha with its organ the Samachar Chandrika. This Samachar Chandrika opposed Ram Mohun Roy`s Bengali Weekly named `Samvada Kaumudi`.

After Ram Mohun`s death in 1833, the Brahmo Samaj had practically no organization, no constitution, no membership, no covenant, and no pledge up to 1841. Maharsi Devendranath Tagore was prominent in the time frame of 1817-1905. He entered the Samaj in 1843 and he gave the Samaj a new life within five years. He introduced a regular form of church service, including thanksgiving, praise and prayer. Previously it was the old practice of mere expositions of passages from the Upanishads attended with sermon and hymn.

Mr. Keshav Chandra Sen was another important member of Brahmo Samaj. His emphasis on Christian and Vaisnava teachings and forms and the rapidity with which social reform was proceeding under his leadership led to a breach with the more conservative members of the Samaj. Keshav Chandra took a leading part in the passing of the Marriage Act of 1872. This act among other things wanted to discourage child marriage, and for the minimum age of men and women marrying under that Act was at eighteen and fourteen years respectively. When Keshav Chandra married his daughter under fourteen to the Maharaja of Cooch-Behar who was below sixteen years of age there was a split in the Samaj. The Samaj actively supported the movement for widow remarriage, abolition of polygamy, women`s education. Thus Brahmo Samaj played a consistent role in the social and religious reforms of the nineteenth century.