Felix is a Professor of Health Psychology within the School of Health Sciences, University of East Anglia, Visiting Senior Researcher at the Behavioural Science Group, University of Cambridge, and Honorary Associate Professor within the Division of Primary Care, University of Nottingham. He has a key research interest in the development and evaluation of mobile phone interventions to promote and support health behaviour change (mHealth), particularly smoking cessation.

Felix has collaboratively developed and evaluated multiple mHealth interventions including individually tailored SMS text messaging systems for smoking cessation (MiQuit and iQuit in Practice systems) and a context aware smoking cessation smartphone app (Quit Sense). He is currently leading research on the development of a face-to-face and digital Nicotine Replacement Therapy (NRT) adherence intervention for pregnant smokers in collaboration with researchers from the University of Nottingham. He is also involved in other mHealth and digital health projects with national and international collaborators and research teams as well as projects exploring the potential of e-cigarettes for pregnancy and postpartum cessation support and understanding dual tobacco and e-cigarette use. Among other methodologies, he specialises in N-of-1 approaches for both observational and experimental investigations.

Felix is a Registered Health Psychologist (Health and Care Professions Council), a chartered member of the British Psychological Society (BPS) and a full member of the Division of Health Psychology (DHP). He is President of the Society for Research on Nicotine and Tobacco in Europe (SRNT-E) and a Senior Fellow of the Higher Education Academy (SFHEA). He was awarded an academic fellowship from the Society for the Study of Addiction (2014-2016) and is an Associate Editor for the journal Addiction. He has served on multiple scientific committees, including the DHP, the European Health Psychology Society (EHPS; co-chair 2022), SRNT-E and the UCL Centre for Behaviour Change Digital Health and Wellbeing conference (co-chair 2019 and 2020). He serves as a standing member of Cancer Research UK’s Expert Review Panel for the Prevention and Population Research Committee (PPRC) panel. He was also a topic expert for the new NICE 'Behaviour change: digital and mobile health interventions' (NG183) advisory committee and currently serves on the 'Tobacco: preventing uptake, promoting quitting and treating dependence' (NG209) NICE committee.