Giles is Professor of Environmental Policy in the Department of Geography and Environment. He is also an Associate of the Grantham Research Institute on Climate Change and Environment at LSE.

An environmental economist by training, Giles has published extensively on the subject of the sustainability of economic development. Much of this research has examined how policy-makers can construct better measures of economic progress through, for example, wealth accounting and natural capital accounting. His work additionally focuses on cost-benefit analysis and the environment, the valuation of natural capital and environmental equity.

Outside of LSE, Giles was a Member of UK Natural Capital Committee during its first phase. He has also been a member of the Policy and Technical Experts Committee (PTEC) for the World Bank's WAVES partnership (Wealth Accounting and the Valuation of Ecosystem Services) as well as the Advisory Board for TEEB (The Economics of Ecosystems and Biodiversity). He is currently a member of Steering Group for the Natural Capital Accounting Project of the ONS (UK Office for National Statistics) and a member of Scientific Committee of the UK Network for Environmental Economists.