Dr. Kumar Hari Rajah began his medical career with housemanship at Seremban General Hospital in 1996, followed by roles as a Medical Officer in emergency units at Kuala Pilah District Hospital and Seremban General Hospital. He continued his training in neurosurgery at Kuala Lumpur General Hospital and completed his Master of Surgery (MS) at University Malaya. Dr. Rajah then served as a General Surgical Trainee at Hospital Kuala Lumpur and Universiti Hospital. His subsequent roles include Consultant General Surgeon at various hospitals such as Selayang General Hospital, Klang General Hospital, and Melaka Manipal Medical College. He has also held academic positions as an Associate Professor at MAHSA University and Perdana University Graduate School of Medicine. Since 2013, he has been practicing at Sentul Medical Centre and QHC Medical Centre, with prior experience as a Consultant at KPMC Puchong Specialist Hospital.