Guy is a Professor of Ecology and the Deputy Head of Life Sciences at Imperial College London. He has more than 25 years of experience in aquatic food web, community, and ecosystems ecology. He has published over 120 peer-reviewed papers and 7 edited books with a focus on environmental stressors in these multispecies systems. Much of his work has aimed to improve our understanding of how complex systems operate in nature, and how they are modified by a range of anthropogenic pressures, including climate change, habitat modification and chemical pollution. He was the Series Editor for Advances in Ecological Research from 2010 to 2019, the British Ecological Society Aquatic Group Leader (2013-16), and a member of the Future Earth ecoSERVICES Scientific Committee.

He currently sits on the Board of Directors of the Freshwater Biological Association and the Meetings Committee of the British Ecological Society. In the last year he has led a £3.7m NERC Large Grant on Gene-to-Ecosystem Impacts of Global Warming, and a £2.4m NERC Emerging Chemical Risks Programme, as well as a range of other projects including a new research programme in Atlantic salmon ecology.