In 1782, Gilchrist was apprenticed as a surgeon's mate in the Royal Navy and travelled to Bombay, India. There, he joined the East India Company's Medical Service and was appointed assistant surgeon in 1784. He marched with the company's Bengal Army to Fatehgarh, and during this journey he noted the extent to which the Hindustani language could be understood in different parts of the country. However, he was surprised that the company neither required nor encouraged their employees to learn it, and subsequent experiences convinced him that officers in the army should also learn it in order to communicate effectively with the Indian soldiers or sepoys.