Upadhyaya, after initially opposing his uncle's conversion, began to study under a Catholic priest and sought conversion, but being denied, sought and received baptism at the hands of an Anglican, after which he was conditionally re-baptized and admitted into the Catholic Church.
After his conversion, Upadhyaya dropped "Brahmo" from his name for religious reasons, and called himself "Bandhab Upadhyaya".
A great intellectual like his uncle, Upadhyay helped lead the effort at bridging the cultural gap between Westernized Christianity in British India and proselytes.
Upadhyaya became famous for dogging Annie Besant and following up on her lectures on Theosophy by giving lectures against Theosophy and in usually the same venues.
Upadhyaya also sought to Indianize Christianity within the limits of orthodoxy. He portrayed himself as a Hindu Christian, positing Hinduism as cultural, not religious, and founded an ashram in Bengal to follow-up on his ideas and experiments.
Upadhyaya wrote in the Sophia, July 1897:
Are we Hindus?
By birth we are Hindus and we shall remain Hindu till death. But as dvija (twice-born), by virtue of our sacramental rebirth we are Catholics, we are members of the indefectible communion embracing all ages and times. In customs and manners, in observing caste and social distinctions, in eating and drinking, in our life and living we are genuine Hindus, but in our faith we are neither Hindu nor European, nor American nor Chinese, but all-inclusive....
The test of being a Hindu cannot therefore be in religious opinions. Yet, we have drunk of the spirit of Hinduism... We agree in spirit with Hindu law-givers in regard to their teaching that sacramental rites (samskaras) are vehicles of sanctification.
With wondering reverence do we look upon their idea of establishing a sacred hierarchy vested with the highest authority in religious and social matters....
Upadhyay was the composer of the hymn Vande Saccidananda ("Saluting the Holy Trinity") and today widely sung during vernacular services in Christian Churches all over India:
Innumerable articles in Bengali and English in short-lived journals and magazines of Bengal such as Sophia, Jote, Sandhya, The Twentieth Century, Svaraj, etc
The Writings of Brahmabandhab Upadhyay (ed. by J.Lipner and G.Gispert-Sauch), 2 vol., Bangalore, 1991 and 2001.
Bibliography
ANIMANANDA, B.: The Blade; Life and work of B. Upadhyay, Calcutta, n.d.
MUKHOPADHYAY, Uma: India's fight for freedom or the swadeshi movement (1905-06), Calcutta, 1958.
LIPNER, Julius J.: Brahmabandhab Upadhyay: the Life and thought of a revolutionary, New-Delhi, 1999.
TENNENT, Timothy C. Building Christianity on Indian Foundations: The Legacy of Brahmabandhav Upadhyay. Delhi: ISPCK, 2000.
SPENDLOVE, Gregory Blake. A Critical Study Of The Life And Thought Of Brahmabandhab Upadhyay. Deerfield: TEDS, 2005.