Dr Headley trained as a specialist in clinical immunology and allergy at several Sydney hospitals gaining experience in treatment of allergic disorders, autoimmune disease, as well as primary and secondary immunodeficiency. He has also worked as a Clinical Research Fellow for the George Institute for International Health.
Dr Headley is qualified as both a fellow of the Royal Australasian College of Physicians (FRACP) and Royal College of Pathologists of Australasia (FRCPA). Dr Headley also work as a Visiting Medical Officer in Clinical Immunology / Allergy at Concord Repatriation General Hospital.