Diabetes mellitus is a metabolic disorder that is linked with many etiologies. It is characterized by chronic hyperglycemia, which interrupts the fat, carbohydrate, and protein metabolism. Lack of insulin production, and impaired insulin sensitivity or insulin resistance are the main factors contributing to dysmetabolism and its complications. Furthermore, uncontrolled diabetes mellitus can cause cardiovascular diseases (CVD). A proper diet can be the management tool for hyperglycemia and its complications as well as for CVD. Several studies have demonstrated the effect of algal bioactive compounds in alleviating different diseases, including diabetes, cardiovascular diseases, and hyperglycemia. In this context, carotenoids, polyphenols, and antioxidant compounds in algae could play a vital role in lowering oxidative stress, leading to diabetes and CVD. Additionally, algal polysaccharides contribute to hypoglycemia by modifying insulin activity and glucose metabolism. Moreover, omega-3 fatty acids, which are necessary for lowering inflammation, improving lipid profiles, and increasing insulin sensitivity, are abundant in algae. Therefore, this chapter discusses how algae-based dietary sources may help to mitigate diabetes and cardiovascular complications.