Gestational diabetes mellitus (GDM) continues to pose a significant challenge to maternal and fetal health, driving the need for advanced diagnostic and therapeutic strategies. Biomarker discovery has proven essential for early detection, mechanistic insights, and targeted interventions. This review provides an in-depth examination of biomarkers related to GDM, focusing on glucose metabolism, insulin resistance, inflammatory signaling, adipokines, oxidative stress markers, and genetic/epigenetic determinants. We also evaluate novel biomarkers emerging from omics technologies and their translational potential in clinical practice. Additionally, we explore the role of microRNAs and extracellular vesicles as emerging biomarkers that could offer new perspectives on GDM pathophysiology. Integration of these biomarkers into predictive models holds the potential to improve risk assessment and patient health outcomes.