On 23 September 1835, Day along with E.L. Abbot and their wives sailed to India for missionary work under the American Baptist Foreign Mission Society (ABFMS).
Upon arrival in Calcutta on 5 February 1836, E.L. Abbot departed to Burma, while the Day family proceeded to Vizagapatam - also known by names Vizag or Visakhapatnam.
[1] Upon arrival in Vizag, Day began learning the local Telugu language and went out on trips with London Missionary Society (LMS) missionaries already active in Vizag from 1805; Chicacole (present Srikakulam) was one town visited by him, that appeared to him to be the right place to commence operations of the "American Baptist Mission."
On 6 June 1836, Roenna Clark bore him first of their seven children - they named the boy after the American Baptist Foreign Mission Board agent in India, Howard Malcom—Samuel Day was not free to choose where they would settle as missionaries - they were bound to wait for the counsel of Howard Malcom.
[1][3] In March 1837, Day was asked by Malcom to work among the English people in Madras (present Chennai) and with a branch of "Maulmein Church" located over there.
He joined Mr. & Mrs. Stephen Van Husen, American missionaries who arrived Nellore in March 1840, and begun working with "Bible Society" [LMS] for a more accurate translation [amend and rewrite] of New Testament into Telugu language—LMS already established the first "Protestant mission" among Telugu speakers in 1805, published Telugu version of New Testament by 1818 and also did rough translation of the Old Testament - In 1836 the first Protestant Chapel among the Telugus was built.
With Roenna left in America, he sailed again to India along with Mr. and Mrs. Lyman Jewett, American missionaries, and arrived Nellore in February 1849 for a five-year term.