Mitochondria are essential organelles in plant cells involved in energy transduction and metabolism. James Whelan has carried out foundation and transformational studies on mitochondria in plant cells by defining the mechanisms and regulation of mitochondrial signalling and biogenesis. These studies have redefined mitochondria from being simply a metabolic hub to that of a central sensor and stress-signalling hub that is critical for plant responses to the environment. His publications, postgraduate student success, early-career researcher mentorship, institutional leadership and international collaborations testify to his international standing as a pre-eminent researcher in mitochondrial biology, an educator and an enthusiast for plant science.