Mary MacLennan is the Senior Advisor on Behavioural Science to the Executive Office of the United Nations Secretary-General, where she leads efforts to integrate behavioural science into the work of the UN. She also heads both the UN Behavioural Science Team and the UN Behavioural Science Group within the UN Innovation Network. In these roles, she supports more than 70 UN Entities across 150+ countries, bringing together a global network of over 8,000 colleagues.

A behavioural scientist with over 15 years of experience, Mary works with governments, international organisations, and other partners to apply behavioural science to real-world challenges - with a particular focus on health, digital decision environments, and institutional design. She has advised the OECD, UN Women, and other global actors, and has played a key role in establishing some of the first behavioural science teams in the public sector and beyond.

Her current work explores how behavioural science can strengthen the use of evidence in complex systems, translate research and technical insight into practice, and inform the design and governance of emerging technologies. She is also a Fellow at the El-Erian Institute of Behavioural Economics and Policy at the University of Cambridge.