A large body of evidence suggests that vegetarian and plant-based diets provide exceptional health benefits, including a reduced risk of obesity, diabetes, heart disease and some types of cancer, and increased longevity. Vegetarian diets are typically lower in fat, particularly saturated fat, and higher in dietary fiber. They are also likely to include more whole grains, legumes, nuts, and soy protein, which together provide micro-nutrients and protective factors at higher levels than most Western diets. In observational studies, a vegetarian or vegan diet is associated with reduced risk of development of type 2 diabetes and lower risk of complications in those with existing diabetes. Although it is often difficult to separate vegetarianism from other healthy lifestyle behaviors, this eating pattern and the absence of red meat and processed meat products may provide particular benefits in the management of diabetes and prediabetes. This article critically reviews the scientific evidence for the role of vegetarian diets in the prevention and management of diabetes.