Observations of comorbidity between disordered metabolism and neuropsychiatric illness have existed for over 100 years. From the first case reports and small cross-sectional studies of the early 20th century through to modern 21st century cohort studies comprising entire populations, evidence has accumulated confirming that metabolic manifestations are a key component of neuropsychiatric illness across the lifespan. Traditionally, observed comorbidity has been attributed to consequences of the illness (e.g., lifestyle factors), treatment (e.g., adverse metabolic effects), or health systems (e.g., health inequalities or diagnostic overshadowing). In recent decades, however, researchers have started to unearth putative pathophysiological links between metabolism and mind, thus heralding promise to transform our understanding of neuropsychiatric illnesses and uncover promising new avenues on how to treat them. Here, research is presented that links body and mind by metabolism at key life phases (pre- and postnatal periods through to older adulthood), with a consideration of the relevant sex differences. Promising strands of basic, epidemiological, and experimental research are presented alongside proposed directions for future research. This article underscores the life-long neuropsychiatric relevance of mitochondrial function, glucose-insulin homeostasis, sex hormones, and the immune system, and how these might be leveraged to develop novel therapies for neuropsychiatric illness.