Magnesium is an essential mineral with several dietary sources including whole-grains, green leafy vegetables, legumes, and nuts. The western diets that are characterized by a high intake of processed foods contribute to a high prevalence of inadequate magnesium intake in industrialized countries. Accumulating data from animal models and small trials in humans support a pivotal role of magnesium in glucose homeostasis, insulin secretion and action. In observational studies, magnesium intake has been inversely associated with insulin resistance, type 2 diabetes mellitus (DM), hypertension, and cardiovascular diseases (CVD). Herein we systematically review the current literature from human population studies on dietary magnesium intake and a host of metabolic disorders, focusing primarily on type 2 DM, hypertension, and CVD. The available evidence indicates that dietary magnesium may favorably affect a cluster of metabolic abnormalities including insulin resistance, hypertension, and dyslipidemia, known as metabolic syndrome. The metabolic syndrome is prevalent worldwide and is associated with greater risks of major chronic diseases, particularly type 2 DM and CVD. Further, available epidemiologic data provide strong support for dietary recommendations to increase consumption of magnesium-rich foods for the primary prevention of the metabolic syndrome and associated chronic diseases. Future studies are warranted to assess the efficacy of magnesium supplementation in the prevention and/or treatment of metabolic syndrome and type 2 DM in human populations.