Abstract The article examines the influence of Swabian Pietism, a variant of Pietism in South Germany, on the Basel Mission’s activities in South India. It highlights how Pietism redefined conversion as a personal, transformative experience, shaping missionary discourse and practices. The Basel Mission, founded by Pietistic followers, exemplifies this approach, emphasising “personal will” in conversion. The Mission’s expansion in 19th-century South India brought encounters with diverse socio-religious groups, including Brahmins, Billavas, and Lingayats, each with distinct responses to Protestantism. These encounters challenge simplistic narratives of religious conversion and transformations, revealing complex negotiations and adaptations by both missionaries and locals. The article argues for an intersectional perspective that considers caste, class, and sectarian divides in understanding missionary encounters. It suggests that notions of ‘native agency’ were nuanced and shaped by social, religious, and economic contexts, leading to a unique ‘Indian’ Pietistic Protestantism that defied missionary expectations of converts.