Prof Hall is internationally recognised for his research on risk analysis and decision making under uncertainty for water resource systems, flood and coastal risk management, infrastructure systems and adaptation to climate change. Professor Hall is a member of the Prime Minister's Council for Science and Technology, is a Commissioner of the National Infrastructure Commission and is Vice President of the Institution of Civil Engineers. He was a member of the UK independent Committee on Climate Change Adaptation from 2009 to 2019 and was Chair of the Science Advisory Committee of the International Institute for Applied Systems Analysis (IIASA) from 2020 to 2022.

Prof Hall's group in the University of Oxford is at the forefront of risk analysis of climatic extremes and their impacts on infrastructure networks and economic systems, from local to global scales. He led the development of the National Infrastructure Systems Model (NISMOD), which was used for the UK's first National Infrastructure Assessment and for analysis of the resilience of energy, transport, digital and water networks in Great Britain. His group developed the first national water resource systems simulation model for England and Wales. Prof Hall conceived of, and now chairs, the UK's Data and Analytics Facility for National Infrastructure (DAFNI). His systems analysis methods have been applied worldwide, including in Argentina, Bangladesh, China, Curacao, Jamaica, Kenya, St Lucia, Tanzania, Uganda and Vietnam, and globally. He has published more than 160 articles in peer reviewed journals, which have been cited more than 15,000 times, and was editor of the journal Water Resources Research from 2017 to 2022.