After King earned his medical qualifications, he began teaching at Peking Union Medical College. Soon after the 1931 Japanese invasion of Manchuria, King moved to Cheeloo University as professor of obstetrics and gynaecology. He held an equivalent post at the University of Hong Kong from 1938. King was named dean of the faculty of medicine in 1940. When the Battle of Hong Kong commenced in December 1941, King began enumerating degrees to be conferred by the university despite the interruption of final exams due to the start of battle. King was not held in Stanley Internment Camp, and remained in his posts at the Tsan Yuk Hospital and Queen Mary Hospital. He also arranged for approximately 140 HKU medical students to continue their studies at institutions in China, among them Kwangsi Provincial Medical College, Lingnan University, National Hsiang Ya Medical College, and Cheeloo University. King himself took a visiting professorship at Shanghai Medical College. King returned to Hong Kong in August 1945, near the end of the Second Sino-Japanese War. He resumed teaching at HKU and aided the reorganization of Hong Kong's health system. King yielded the deanship in 1949, only to retake the role between 1951 and 1954. In the 1953 Coronation Honours, King was named an Officer of the British Empire. Between 1954 and 1955, he was pro vice chancellor of Hong Kong University.