Gestational diabetes mellitus (GDM) is defined as 'carbohydrate intolerance resulting in hyperglycemia of variable severity with onset or first recognition during pregnancy'. GDM is associated with several detrimental health consequences during pregnancy and delivery for both mother and baby. The largest public health impact of GDM is through its role on future diabetes in the mother and obesity and diabetes in the offspring. Physical activity (PA) is likely an effective intervention for prevention and treatment of GDM, given its known effectiveness in prevention and treatment of type 2 diabetes. Based on observational studies, PA initiated before and/or during pregnancy has a positive influence on maternal glucose and insulin metabolism and reduces the risk of GDM. However, although PA interventions have been reported to be effective at improving glycemic control in women who already developed GDM, prenatal PA interventions aimed at preventing GDM have shown modest effectiveness in increasing PA levels and thus were not effective in improving glucose/insulin metabolism or reducing GDM incidence. There is therefore a strong need to develop effective strategies for increasing PA levels, especially in women at high risk for GDM who are often obese and inactive. The optimal intervention for preventing or managing GDM is still unknown, and further studies are needed to determine the type, intensity, frequency and duration for the most successful PA intervention. Furthermore, the effects of PA on neonatal outcomes are not clear, and it is highly recommended that future studies examine more specific neonatal outcomes such as body composition.