Nature offered several benefits in the form of herbal plants to treat a variety of disorders. This chapter provides an overview of the secondary metabolites, which are unique organic compounds produced by plants, microorganisms, and fungi that are not directly involved in primary growth but play important roles in their ecological adaptation. Their important characteristics, such as structural diversity and biosynthetic processes, are discussed, and their functions in defense, ecological interactions, and evolutionary adaptations are emphasized. The chapter also focused on the important role of secondary metabolites in diabetes control and antioxidant, anti-inflammatory, and enzyme-inhibiting properties. Important classes such as phenolic compounds, flavonoids, alkaloids, terpenoids, saponins, polysaccharides, steroids, and coumarins are also explained for their role in blood glucose control, improving insulin sensitivity, and preventing diabetes-related processes. The review covers metabolites of plant, microbial, and fungal origin, including specific cases, therapeutic possibilities, and mechanisms of action. By focusing on biochemical, pharmacological, and ecological sides, this chapter will explain the secondary metabolites as a potential source for creating new antidiabetic drugs.