Professor Llewellyn has an international reputation in the theory and practice of financial regulation, the analysis of financial crises, and the business strategies of financial institutions.

He has previously worked at the UK Treasury and the International Monetary Fund and has been a consultant to several international organisations in the theory and practice of financial regulation, and to financial firms in the area of business strategies. 

Until recently he was Chairman of the Banking Stakeholder Group of the European Banking Authority (the pan-EU regulatory agency for banking).  He previously served as a Public Interest Director of the UK’s Personal Investment Authority which was responsible for the regulation of retail financial services until succeeded by the Financial Services Authority.

He has published widely (including over 20 books) in the areas of financial regulation, financial crises, and business strategies and models of financial firms. He serves on the editorial boards of several finance journals an often contributes to media outlets.