Simon Day is from the United Kingdom. He serves as a senior advisor at the Behavioural Insights Team and before worked at the Foreign and Commonwealth Office.

As a British diplomat he gained extensive experience in Africa (West Africa, Ethiopia and Djibouti), the Middle East (at the UN Security Council in New York), and the EU. He has worked on a cross range of issues, including: conflict resolution; sanctions; EU reform; public diplomacy; development work; and peacekeeping. Simon holds a Master of Arts in History from the University of Oxford. He speaks fluent French.