The Garo, a matrilineal tribal society of the Garo Hills of Meghalaya and adjoining districts of Assam and Bangladesh, moved within a century and a half from an almost universal adherence to the indigenous Songsarek faith to a population that is today overwhelmingly Christian. This paper traces that transformation through documentary and secondary historical sources, situating it within debates on missionary encounter, indigenous agency, and cultural continuity in tribal Northeast India. Rather than reading Garo Christianity as the straightforward outcome of American Baptist missionary initiative, the paper foregrounds the role of native evangelists — most notably Omed Watre Momin and his nephew Ramke Watre Momin, and the native colporteurs and preachers who followed them — whose baptism in the early 1860s and subsequent preaching at Rajasimla inaugurated an indigenously mediated movement that missionaries such as Miles Bronson and Issachar Jay Stoddard later helped consolidate into a permanent mission station at Tura. The study traces the institutional pathway from the first Rajasimla congregation (1867) through the founding of the Garo Baptist Convention, mission schools, vernacular Bible translation and the Harding Theological College, and examines the later arrival of Catholic, Adventist and other denominations. It further asks how core elements of Songsarek cosmology and Garo matrilineal kinship — most visibly the Wangala harvest festival — have persisted alongside, and been absorbed into, Christian practice, and situates the Garo case comparatively against the Welsh Presbyterian mission among the neighbouring Khasi. The paper argues that Garo Christianity is best understood as a negotiated and indigenously mediated transformation rather than as a straightforward colonial imposition.