A/Prof Ong Thiew Chai is a Senior/Emeritus Consultant with the Department of Psychiatry, Tan Tock Seng Hospital. His clinical interest is in General Psychiatry in hospital practice with special interest in clinical hypnotherapy. He is involved in inpatient care and in the outpatient clinics. He is also involved in teaching junior staff as needed.

A/Prof Ong obtained his MBBS in 1970. His other qualifications include Diploma in Psychological Medicine from The Royal College of Physicians of London and The Royal College of Surgeons of England in July 1978. In December 1978 he obtained his MRCPsych, Member of the Royal College of Psychiatrists, United Kingdom. In September 1981 he obtained his FAMS, Fellow of the Academy of Medicine, Singapore. In February 1999 he was awarded his FRCPsych, Fellow of the Royal College of Psychiatrists, United Kingdom.

A/Prof Ong has served in various appointments including National Heart Centre as visiting consultant, specialist member of Civil Aviation Board, member of Drug Rehabilitation Centre Review Committee, and Senior Consultant for Addiction Services at Ministry of Health. He has been past President of Singapore Psychiatric Association and past President of Chapter of Psychiatrists, Academy of Medicine. He has served in community work in Jesus Saves Mission clinics from 1971 to 1975.

A/Prof Ong's awards include Long Service Awards from TTSH, Long Service Awards from Drug Rehabilitation Centre Review Committee, NHG Health Outstanding Citizenship Award, Emeritus Teacher Award from TTSH, Emeritus Consultant Award from TTSH, Lee Foundation NHG Health Lifetime Achievement Award, and Outstanding Psychiatrist Award from Singapore Psychiatric Association. His national awards include Pingat Pentadbiran Awam (Gangsa) on 9 August 2005 and Pingat Bakti Masyarakat on 9 August 2008.