Gestational diabetes mellitus (GDM) is one of the most common metabolic complications of pregnancy, characterized by glucose intolerance with onset or first recognition during gestation. The increasing prevalence of GDM parallels rising rates of obesity, sedentary lifestyles, and poor dietary patterns, posing significant risks to both maternal and fetal health. Conventional management strategies include dietary modification, physical activity, glucose monitoring, and pharmacotherapy when necessary. In recent years, growing attention has been directed toward functional foods and bioactive compounds as adjunct nutritional interventions for GDM management. Functional foods rich in dietary fibre, probiotics, polyphenols, omega-3 fatty acids, and low-glycemic carbohydrates have demonstrated beneficial effects on glycemic control, insulin sensitivity, lipid metabolism, inflammation, and oxidative stress. Bioactive compounds such as flavonoids, phenolic acids, carotenoids, and short-chain fatty acids exert mechanistic effects through modulation of gut microbiota, enhancement of insulin signaling, reduction of oxidative damage, and regulation of inflammatory pathways. Evidence from observational studies, randomized controlled trials, and meta-analyses suggests that targeted inclusion of functional foods—such as whole grains, legumes, fermented foods, fruits, vegetables, and nuts—can improve fasting and postprandial glucose levels while reducing adverse pregnancy outcomes. This review summarizes current evidence on the role of functional foods and bioactive compounds in the nutritional management of GDM and highlights their potential as safe, cost-effective, and sustainable strategies to support maternal metabolic health.