Dr Llewellyn is a Partner in Llewellyn Consulting. Llewellyn Consulting specialises in macroeconomics and the economics of climate change.

Dr Llewellyn, a New Zealander, received his undergraduate degree at the Victoria University of Wellington, New Zealand, and his Doctorate at the University of Oxford. In 1970 he was appointed a Research Officer in the Department of Applied Economics at the University of Cambridge. From 1972 he was a Fellow of St John's College, Cambridge, and in 1974 he was appointed Assistant Director of Research in the Faculty of Economics at Cambridge. He then spent seventeen years at the Organisation for Economic Cooperation and Development (OECD) in Paris, where he was in charge of international economic forecasting and policy analysis; editor of the OECD Economic Outlook, then Deputy Director for Social Affairs, Manpower and Education, and finally Head of the Secretary General's Private Office (Chief of Staff).

From 1995 to 2008 he was at Lehman Brothers, first as Chief Economist Europe, then as Global Chief Economist, and finally as Senior Economic Policy Advisor.

Dr Llewellyn has published widely, including on: international economic policymaking and co-ordination; economic forecasting; climate change; population ageing; and the Iraq war. Together with two former colleagues, he has published two books: one on the international aspects of forecasting, modelling, and economic co-operation; and the other on economic policies for the 1990s. In 2007 Lehman Brothers published his report 'The Business of Climate Change: Challenges and Opportunities' and its sequel 'The Business of Climate Change II'; also in 2007, Lehman Brothers published 'India: Everything to Play for'. In 2008 Nomura International published his report 'The Business of Ageing'.

Dr Llewellyn is a member of the International Advisory Board of the Harvard Environmental Economics Program; Secretary of State's Panel on Monitoring the Economy, UK Department of Business Enterprise and Regulatory Reform; International Advisory Board of the Kuwait Petroleum Corporation; Trustee of the FIA Foundation for the Automobile and Society; and Adjunct Professor at Imperial College, London.