Judy Hirst is a physical chemist who combines structural, biochemical and chemical techniques to pioneer studies of energy conversion in complex redox enzymes: how they capture the energy released by a redox reaction to power proton translocation across a membrane, or catalyse the interconversion of chemical bond energy and electrical potential. She is known particularly for her work on the mechanisms of catalysis and reactive oxygen species production by mammalian respiratory complex I (NADH:ubiquinone oxidoreductase), an energy-transducing, mitochondrial redox enzyme of fundamental and medical importance, and for solving its structure by electron cryomicroscopy. Judy is currently Deputy Director of the MRC Mitochondrial Biology Unit at the University of Cambridge, and Fellow of Corpus Christi College in chemistry. She was awarded the Royal Society of Chemistry Norman Heatley Award in 2012 and chaired the Gordon Research Conference on Bioenergetics in 2017.