Although women with gestational diabetes mellitus (GDM) are advised to incorporate physical activity into their lifestyle in order to reduce their risk of developing type 2 diabetes (T2DM), it is recognized that new mothers face barriers to postpartum exercise. Thus, we sought to determine whether, following the diagnosis of GDM, women indeed alter their postpartum physical activity patterns, as compared to their peers without GDM. In this prospective observational cohort study, we assessed the physical activity patterns of 238 white women (58 with GDM, 180 without GDM) in the year before pregnancy and in the year following delivery, using the Baecke questionnaire, which evaluates the following three domains of physical activity: work, sport activity, and nonsport leisure-time activity. Before diagnosis with GDM, women reported lower pregravid sport (P = 0.010) and leisure-time activity (P = 0.013), compared to their peers without GDM. By 1 year postpartum, however, there were no longer significant differences between the GDM and non-GDM groups in either sport or leisure-time activity (P = 0.078 and P = 0.957, respectively). In particular, women with GDM significantly increased their leisure-time activity over the first year postpartum (F = 10.1, P = 0.002), whereas the non-GDM group did not (F = 0.00, P = 0.984). Indeed, on multiple linear regression analysis, GDM independently predicted an increase in leisure-time activity between 1 year pregravid and 1 year postpartum (t = 2.55, P = 0.012). Furthermore, this significant relationship persisted even after adjustment for the finding of prediabetes/diabetes at 3 months postpartum (t = 2.83, P = 0.005). In conclusion, women with GDM successfully increased their leisure-time activity in the first year postpartum, reflecting an element of lifestyle change following this diagnosis.