After completing his undergraduate medical degree (MBBS) at University of Queensland, Brisbane, Australia, Dr. Ooi undertook his postgraduate training in Gastroenterology / Hepatology / Internal Medicine) in Brisbane, Australia and in Auckland, New Zealand. He did his Hepatology Fellowship at the New Zealand Liver Transplant Unit.
Dr. Ooi was appointed Consultant Gastroenterology / Physician at the North Shore and Middlemore Hospitals in Auckland before returning to Penang where he joined Penang Medical College as Associate Professor of Medicine. At the same time, he was the visiting Consultant Gastroenterologist at the Penang General Hospital.
Dr. Ooi was the ex-treasurer and ex-committee member for the Malaysian Society of Gastroenterology and Hepatology. He was the Principal Investigator for several international multicentre trials in Hepatitis B.