Professor Mendis graduated from university of Colombo in 1971 and completed his professional training in psychiatry in Sri Lanka and in the United Kingdom where he obtained the membership and later the Fellowship of Royal College of Psychiatrists in 1978 and 1987. Subsequent exposure to special areas of mental health, social science, curriculum and health policy developments at Harvard Medical School, Centre for Addiction and Mental Health in Toronto, University of Connecticut and a number of other leading centres in several countries gave him the opportunity to widen the scope of his academic and professional work.
He joined the Department of Psychiatry, University of Colombo in 1974 and was appointed to the Chair in 1989. He was appointed as a Senior Professor in 1997 and retired as the emeritus Professor of psychiatry in 2011. During his tenure in the university, apart from carrying out teaching, training, research and development activities he was the Senior Consultant Psychiatrist of the University Psychiatry unit of the National Hospital Colombo.
Dr. Mendis has been in the forefront of several development activities. In the medical school as the chairman of the curriculum development committee he took the initiative and gave the leadership to bring about significant changes in the medical curriculum which led to the medical school adopting a new systems based curriculum in 1994. During his tenure as the Head of the Department Psychological Medicine, clinical attachment I psychiatry was extended to two months and psychiatry was made a separate subject with independent evaluation at the final MBBS examination. Â The scope of the department was widened by renaming it as Department of Psychological Medicine and establishing academic positions in specialized areas. There had been significant reforms in the research ethics committee during his tenure as its chairman.
His major achievement in the field of psychiatry has been the development of community psychiatry by establishing the National Council for Mental Health (NCMH) in 1982. This non government organisation introduced and supported a number of activities to raise the status of psychiatry and to develop new community based services through its two pioneering mental health resource centres at Borella and Gorakana. Â Apart from triggering the development of many new community organizations a large number of mental health professionals and the community benefitted from this activity. NCMH together with the ministry of health with the World Bank funding initiated the introduction of Medical Officer of Health programme which has become an important component of district mental health service activities.
Dr. Mendis established the Health Development and the Research Programme of University of Colombo in Collaboration with University of Bergen Norway. This programme organized the Postgraduate Diploma course in Health Development. He was a member of the Presidential Task Force on Health Policy in 1997. He also served as a member of the Board of Management of the Postgraduate Institute of Medicine, University Council and the National Science and Technology Commission.
He was associated with the formation of the South Asian Forum for Mental Health and was its founder president. He is a founder member of the World Association for Psychosocial Rehabilitation and later the Regional Vice President and a Board Member. Dr. Mendis has a number of publications in scientific journals, has contributed to many international meetings and has been a short term consultant to WHO at its expert committees and the mental health development programme in Cambodia.