From 1830 to 1834, he apprenticed under Walter Henry Medhurst, who taught him Bible translation, village preaching, hospital chaplaincy, teaching, printing, book binding, lithography and literature distribution.
In September 1939, due to his fluency in Malay, he was invited to join the Singapore branch of the London Missionary Society as an agent.
He founded the Prinsep Street Presbyterian Church, initially known as the Malay Mission Chapel and popularly called the "Tuan Keasberry puna Graja", in August 1843 as he believed that a larger meeting space was required.
[3] [2] Keasberry established a school for Malay boys in a shophouse on Rochor Road in 1840 with 12 Orang Laut students, who were taught reading, writing, geography, arithmetic, music, Bible scriptures, and later natural sciences and English In the same year, he began printing educational materials with a lithographic press borrowed from missionaries of the American Board of Commissioners for Foreign Missions.
Among the first publications that he published and printed was The Child's Picture Defining and Reading Book by Thomas Hopkins Gallaudet, which he had translated into Malay, and Kitab Darihal Tabiat Jenis-Jenis Kejadian Iaitu Guna Bagi Kanak-Kanak.
In 1848, he moved the boarding school to a larger location on River Valley Road, and hired Munshi Abdullah as a teacher.
[2][3] Keasberry was commissioned by the British and Foreign Bible Society to translate the New Testament to Malay, and he did so with the assistance of Munshi Abdullah, printing it in 1853.