 Caldwell left university with a distinction and was ordained as a Congregationalist minister.At 24, Caldwell arrived in Madras on 8 January 1838 as a missionary of the London Missionary Society and later joined the Society for the Propagation of the Gospel Mission (SPG).To further his missionary objectives, Caldwell realized that he had to be proficient in Tamil to proselytize the masses and he began a systematic study of the language.