Dr Samarasinghe grew up in South London attending secondary school at Dulwich College before moving on to medical school at Charing Cross and Westminster (now part of Imperial College, London).
Dr Samarasinghe qualified in 1995 then did his junior doctor training in a variety of London teaching hospitals as well as hospitals in Surrey (including an inspiring year at Frimley Park). Choosing to specialise in Medicine as a registrar, with specialist interests of Clinical Pharmacology and Diabetes, he spent an initial 4 years at Chelsea and Westminster Hospital prior to moving to King's College Hospital in South London. Whilst there for 2 and a half years, he pursued a Wellcome funded MD research project in diabetes, under the auspices of Professor Stephanie Amiel, investingating the role of glucose and insulin resistance on the brain's higher appetite functions utilising functional MRI.
He returned to Chelsea and Westminster to complete his training as a senior registrar before gaining consultant status. He was appointed a Consultant in Acute Medicine with a specialist interest in Diabetes and Clinical Pharmacology at Frimley Park Hospital in 2009.