Reay's research focuses on greenhouse gas fluxes and land use , including national and international research projects such as CarboEurope and NitroEurope, and research council-funded work through the UK's Natural Environment Research Council. Reay's key peer reviewed publications include novel work on global carbon sinks, the soil methane sink, and nitrous oxide emissions from aquatic systems. His work on nitrous oxide featured in the Intergovernmental Panel on Climate Change's Fourth Assessment Report. In addition to his contributions to the understanding of greenhouse gas fluxes, Reay has written widely on climate change policy and society, particularly on individual and community action 
Reay has authored several books on climate change, including the popular science books Climate Change Begins at Home published in 2005 by Macmillan and shortlisted for the Times Higher Young Academic Author of the Year Award, and Your Planet Needs You!  published in 2009 by Macmillan Children's Books. He is also lead editor of Greenhouse Gas Sinks  published in 2007 by CABI and creator and editor of the climate change science website Greenhouse Gas Online . Publication list at University of Edinburgh .
Reay is programme director of the MSc in Carbon Management at the University of Edinburgh  and co-director of the Foreign and Commonwealth Office Chevening programme Finance and Investment in a Low Carbon Economy.
He is very active in climate change knowledge exchange, both nationally and internationally , being a regular media commentator on climate change issues, advising on and appearing in the BBC's Can We Save Planet Earth Are We Changing Planet Earth?#Can We Save Planet Earth? film with Sir David Attenborough, and having provided expert evidence on climate change to select committees in the Westminster and Holyrood Parliaments.. Knowledge exchange information, University of Edinburgh . Reay currently sits on the British Council Scotland Advisory Committee as their climate change expert .
- Chris Goodall. Book Review: Going in the right direction, Nature Reports Climate Change, doi:10.1038/climate.2007.45.
- Brian Clegg. Review - Climate Change Begins at Home Popular Science.
- Chew Hung Chang. BOOK REVIEW: "Climate Change Begins at Home The Singapore Economic Review, 2008, vol. 53, issue 02, pages 337-338.
- Irena Dingley. Cut Your Carbon BBC.