During the
Japanese occupation, Shanmugaratnam worked as a laboratory technician to avoid being conscripted by the Japanese forces as a manual labourer. After obtaining his medical licence, he joined the Government Medical Service as a pathologist. As a researcher, his main area of expertise was in
nasopharyngeal carcinoma, a type of cancer with high incidence rates in Southeast Asia and southern China, where a large percentage of the regional ethnic Chinese diaspora trace their ancestry to. Shanmugaratnam was a contributor to the development of medical education in Singapore, specifically postgraduate training for licensed local doctors. During the late 1960s, then-Deputy Prime Minister
Toh Chin Chye, a former academic at the University of Singapore, made local headlines for censuring the university's medical faculty over their failure to formalise postgraduate medical education and the awarding of local qualifications; he specifically requested Shanmugaratnam, then the Master of the
Academy of Medicine, to chair a committee which would oversee this endeavour. This was achieved by 1970 and allowed local doctors to complete
specialty training in domestic hospitals under the auspices of the university, with external validation from regulatory bodies in the United Kingdom and Australia, rather than the costlier option of spending several years abroad. He was appointed Emeritus Professor by NUS in 1986 and continued to lecture and conduct seminars into his early nineties. Throughout the course of his career, he had been a member of various committees and bodies, such as the Academy of Medicine, the Singapore Medical Council and the
Union for International Cancer Control. ==Personal life==