John Gilchrist was principally known for his study of the Hindustani language, which was adopted as the lingua franca of northern India (including what is now present-day Pakistan) by British colonists and indigenous people. He compiled and authored "An English-Hindustani Dictionary", "A Grammar of the Hindoostanee Language", "The Oriental Linguist", and many more. His lexicon of Hindustani was published in the Perso-Arabic script, Nāgarī script, and in Roman transliteration. He is also known for his role in the foundation of University College London and for endowing the Gilchrist Educational Trust.