Rashan trained in medicine at the University of Colombo and subsequently completed training as a critical care physician and anaesthetist in the UK.

Rashan was awarded a PhD scholarship by the University of Oxford, where his doctoral work was on developing methods for continuous healthcare evaluation in resource-limited settings. During this time he co-founded NICS-MORU, a not-for-profit research unit based in Sri Lanka that develops and curates digital registries to strengthen research capacity and facilitate data-driven service improvement in Asia and Africa. NICS-MORU also functions as the data coordinating centre for multinational observational and interventional research projects. He has also completed an MSc in Clinical Trials at London School of Hygiene and Tropical Medicine.

Rashan works clinically as a consultant in intensive care medicine at the General Sir John Kotelawala Defence University Hospital, Sri Lanka and at University College Hospitals London.