Type 2 diabetes (T2D) is one of the most prevalent metabolic disorders in the United States. Increased blood glucose levels and improper crucial metabolism ensuing from insulin action, insulin secretion defect, or both are characteristics of this disease. The risk of developing T2D is associated with many factors, including obesity, race, inactivity, and genetics. Increased whole-grain (WG) consumption has been reported to lower the risk of obesity and T2D. Among WGs, barley shows a comparative advantage in its fiber content, especially the soluble fiber, beta-glucan (β-glucan), an active component credited for this benefit. Barley also contains important phytochemicals, mostly intertwined with its fiber, reported to also offer glycemic response benefits. The mechanism by which barley exerts these changes in glycemic response is not entirely understood. However, the physical properties of barley fiber, the function of microbial metabolites of fiber, short chain fatty acids, and the beneficial effects of its phytochemicals through multiple pathways have all been reported as the potential mechanisms for its antidiabetic effects. This review summarizes recent studies concerning the health-promoting benefit of barley in preventing and moderating the risk factors associated with diabetes and the potential underlying mechanisms.