Dr. Leong graduated from the University of Malaya in 1993 and completed his Master of Internal Medicine in 2001. He had his Infectious Diseases training under Datuk Dr. Christopher in Kuala Lumpur Hospital in 2001 and was involved in managing Severe Acute Respiratory Syndrome (SARS) outbreak in Kuala Lumpur Hospital in 2003. Subsequently, he went to Royal Melbourne Hospital in Australia for Infectious Diseases attachment in 2004. After coming back from Australia, Dr. Leong worked at Sultanah Aminah Hospital, Johor Bahru, and Sungai Buloh Hospital. He was transferred back to Kuala Lumpur Hospital in 2014 and was appointed as the Chairman of the Infection Control and Antibiotic Committee in 2019.