He graduated from University College Dublin Medical School in 1998 and completed a PhD in cardiovascular physiology at Oxford University as a Rhodes Scholar (1992-1995). He trained in general medicine and cardiology in London, followed by subspecialty training in cardiac electrophysiology at St Mary’s Hospital. From 2005-2006, Dr O’Neill completed a clinical research fellowship in Bordeaux with Professors Michel Haïssaguerre and Pierre Jaïs where began his interest in atrial arrhythmias. In October 2009, he joined St Thomas’ Hospital and King’s College London in the Department of Cardiology and School of Imaging Sciences and Biomedical Engineering and was promoted to Reader in 2011 and Professor in 2013. He is the Departmental Lead for Arrhythmias in Adult Congenital Heart Disease, the Divisional Research. Lead for Electrophysiology and the Joint Clinical Director for the Cardiovascular Division. His primary research interests are the development and use of advanced signal processing and imaging technologies to improve arrhythmia characterization and treatment in patients with heart rhythm disturbances.