Aim. To synthesize evidence on the role of physical activity (PA) in preventing and managing gestational diabetes mellitus (GDM), covering physiology, observational data, trials, implementation barriers, and gaps. Materials and methods. Narrative review of studies on preconception and pregnancy PA for GDM prevention and on PA interventions for treatment/control. Outcomes: incident GDM, fasting/postprandial glucose, insulin use, gestational weight gain, hypertensive disorders, delivery mode, neonatal outcomes (LGA, macrosomia, hypoglycemia), and longer‑term offspring data. Dose–response and subgroup analyses by timing, intensity, supervision, and maternal BMI. Results. Preconception and early‑pregnancy PA are linked to lower GDM risk Protective estimates span ~21–46% overall. Dose–response: ≥15–21 MET h/week preconception; in pregnancy, 10/20/50 MET h/week ≈6/11/15% lower risk. Early, supervised light–moderate programs yield the largest prevention effects; one RCT reported up to 90% risk reduction at 150–180 min/week. A single moderate bout lowers postprandial glucose for 1–2 h; repeated aerobic/resistance training with dietary counseling improves fasting/postprandial glucose and may reduce insulin needs. Intensified lifestyle care reduces gestational weight gain and LGA. Evidence for hypertensive disorders, cesarean delivery, and long‑term outcomes is mixed. PA levels are low (MVPA ~11–14 min/day); barriers are clinical, symptomatic, cultural. Conclusions. Promote PA before and early in pregnancy (≥15–21 MET h/week preconception; up to ~50 MET h/week in the first trimester when feasible). Early, supervised light–moderate programs and regular aerobic or resistance exercise plus dietary counseling are effective. More RCTs should refine optimal modality, dose, timing, supervision, and long‑term outcomes.