Hypomagnesemia is 10-fold more common in individuals with type 2 diabetes (T2D) than in the healthy population. Factors that are involved in this high prevalence are low Mg2+ intake, gut microbiome composition, medication use, and presumably genetics. Hypomagnesemia is associated with insulin resistance, which subsequently increases the risk to develop T2D or deteriorates glycemic control in existing diabetes. Mg2+ supplementation decreases T2D-associated features like dyslipidemia and inflammation, which are important risk factors for cardiovascular disease (CVD). Epidemiological studies have shown an inverse association between serum Mg2+ and the risk of developing heart failure (HF), atrial fibrillation (AF), and microvascular disease in T2D. The potential protective effect of Mg2+ on HF and AF may be explained by reduced oxidative stress, fibrosis, and electrical remodeling in the heart. In microvascular disease, Mg2+ reduces the detrimental effects of hyperglycemia and improves endothelial dysfunction; however, clinical studies assessing the effect of long-term Mg2+ supplementation on CVD incidents are lacking, and gaps remain on how Mg2+ may reduce CVD risk in T2D. Despite the high prevalence of hypomagnesemia in people with T2D, routine screening of Mg2+ deficiency to provide Mg2+ supplementation when needed is not implemented in clinical care as sufficient clinical evidence is lacking. In conclusion, hypomagnesemia is common in people with T2D and is involved both as cause, probably through molecular mechanisms leading to insulin resistance, and as consequence and is prospectively associated with development of HF, AF, and microvascular complications. Whether long-term supplementation of Mg2+ is beneficial, however, remains to be determined.