Professor Sir John Walker FRS was born in Halifax, Yorkshire and attended Rastrick Grammar School.  He studied chemistry at St Catherine’s College Oxford, and in 1969 was awarded the D Phil degree for studies of antibiotics at the Sir William Dunn School of Pathology in Oxford. During periods of research at the University of Wisconsin USA, and The Pasteur Institute in Paris he cultivated his expertise in the analysis of proteins, and in 1974, he joined The Medical Research Council (MRC) Laboratory of Molecular Biology in Cambridge. Here, he developed his interest in the mitochondria, special compartments (organelles) in our cells best known for their role as powerhouses, as they breakdown food molecules and turn out ATP (adenosine triphosphate). Each of us makes 60 kg of ATP daily to provide the energy in a form suitable for sustaining our lives. Whilst studying the features of  DNA molecules found in the mitochondria, he became interested in the question of how energy in food is transferred into ATP. Thus, in 1978, he began characterizing the gigantic enzyme called ATP synthase that makes ATP in the mitochondria of mammalian cells. By 1992, John had realised that the ATP synthase is molecular machine, and that the energy released from food intake drives the synthesis of ATP by a mechanical rotary mechanism. This work led to the award of the Nobel Prize in Chemistry in 1997. In the same year, John was elected as a Fellow of Sidney Sussex College.

In 1998, John was appointed as Director of the MRC Dunn Human Nutrition Unit, which, in 2008, became the MRC Mitochondrial Biology Unit, and since 2013, he has been the Director Emeritus. Here, he has continued to delve deeper into the mechanism of the ATP synthase, and especially into the question of how the turning of the machine's rotor is generated. His description in 2021 with colleagues of the atomic structure of the complete dimeric mitochondrial ATP synthase has provided crucial evidence that rotation is generated by the direct application of a voltage to the enzyme's rotor via a Grotthus chain of water molecules. His current interests include working out how the ATP synthase machine is assembled within the mitochondria.

John was and remains a strong advocate of linking research into mitochondria with neuromuscular and neurodegenerative disease  and ageing, and he uses his knowledge about energy conversion for medical benefit, in 2021 establishing the structure of the mycobacterial ATP synthase as a target for developing new drugs against tuberculosis. Another of his activities is to act as Chair of the Scientific Supervisory Board of the Citrin Foundation.

John is a Fellow of the Royal Society, and in 2012, he was awarded the Copley Medal, the UK's highest scientific accolade. He is also a Fellow of the Academy of Medical Sciences, an Honorary Fellow of St Catherine’s College, Oxford, a Foreign Member of L’Accademia Nazionale dei Lincei, of the Royal Netherlands Academy of Arts and Sciences, and of The Royal Society of New Zealand, and a Foreign Associate of the US National Academy of Sciences. He has been awarded fifteen honorary doctorates from Universities around the world.