Type 2 diabetes mellitus (T2DM) is a metabolic disorder characterized by severe metabolic disarray in patients. This disruption not only affects glucose metabolism but also alters the composition of the native gut microbiota. Current research indicates that the gut microbiome of T2DM patients is distinctive, with dysbiosis being closely associated with insulin resistance, pancreatic inflammation, and the development of microvascular and macrovascular complications related to diabetes. This review aims to delve into the molecular mechanisms by which the gut microbiota and their metabolites influence the onset and progression of T2DM. It emphasizes the role of beneficial and potentially harmful bacteria in disease development and provides a detailed discussion on the impact of key metabolites such as short-chain fatty acids (SCFAs), trimethylamine N-oxide (TMAO), secondary bile acids, and hydrogen sulfide (H₂S). These metabolites affect intestinal barrier function, systemic inflammation, and the maintenance of glucose homeostasis through various signaling pathways. Through these analyses, the review seeks to offer new perspectives and strategies for the prevention and treatment of diabetes. It hopes to contribute to the clinical management of the disease by modulating gut microbiota balance and intervening in metabolite production, thereby delaying the progression of diabetes and reducing the incidence of complications, potentially providing new targets for clinical therapy.