Being the son of the prominent British missionary Walter Henry Medhurst, the younger Medhurst was educated at Blundell's School and in Macau. There he acquired a good command of Chinese, Dutch and Malay. In October 1840, he was appointed Chinese secretary to the British superintendent of trade in China. He was sent along with other to inspect the newly-acquired colony of British Hong Kong in early 1841. During the Opium War, he worked under Rear-Admiral George Elliot and Sir Henry Pottinger.