Having joined the Foreign Service in 1891 as a temporary library clerk, Severn was appointed, in 1894, private secretary to Sir Charles B H Mitchell, then Governor of the Straits Settlements. After a period of 17 years in the colonial administration of the Federated Malay States including four years as private secretary to Governor Sir John Anderson, he was appointed Colonial Secretary in Hong Kong, leading the administration under Governor Sir Frederick Lugard. He was acting governor of Hong Kong for just over a year during a transition between governors from 1918 to 1919. It was 1918 when he entertained the visiting George Morrison, the highly influential Political Advisor to the President of the Chinese Republic, who related that the appointment of the "Buffoon of Hong Kong" was "one of the jokes of our time".