After an academic career mainly at Imperial College London, he was appointed in 2008 as the Government Chief Scientific Advisor reporting directly to the Prime Minister. He worked for both Gordon Brown and David Cameron. He retired from the position in 2013.

As GCSA, he was responsible for increasing the scientific capacity across Whitehall by encouraging all major departments of state to recruit a Chief Scientific Adviser. While GCSA he set up the Scientific Advisory Group in Emergencies (SAGE) that reported to the COBRA committee.

He is Professor of Natural Resource Management and Senior Fellow of the Martin School at Oxford University. Other roles have included Chair of the UK Meteorological Office, retiring in 2019. He is currently Chair of Rothamsted Research, the Environmental Advisory Committee to Rolls-Royce, the Independent Advisory Board to Drax power and the Systemic Risk Centre at the London School of Economics.

He has chaired the Global Panel on Agriculture and Food Systems for Nutrition since 2013.

He was awarded a knighthood by the Queen in 2010 and the Order of the Rising Sun by the Japanese Government in 2014. This latter award was for work providing advice on the Fukushima nuclear incident. He has recently chaired a Commission on Technology-Critical Metals which reported in 2021.