Women with gestational diabetes mellitus (GDM) have a high risk of developing type 2 diabetes (T2D). Readiness for behaviour change to mitigate this risk may be low after pregnancy and may further decrease over time without appropriate interventions. This study aimed to evaluate readiness for behaviour change in the first and second postpartum years in women with recent GDM to determine the best timing for lifestyle interventions to prevent T2D. This study included a subset of women with GDM between 2009 and 2013 in Ontario, Canada from a larger prospective cohort study who completed a survey in the first and second postpartum years (N = 329). The primary outcome was stage of readiness for behaviour change for diet and physical activity, compared between the first and second postpartum years. The mean age was 34.3 ± 4.4 standard deviation (SD) years and mean pre-pregnancy body-mass index (BMI) was 26.7 ± 6.9 kg/m2. In the first postpartum year, 86% of women reported a pre-action stage of change, which was 87% by the second postpartum year (p = 0.646). Non-Caucasian ethnicity was associated with lower odds of being in the action stage of readiness for behaviour change overall and for physical activity in both time periods. Most postpartum women with recent GDM are in a pre-action stage of change after delivery, which does not increase by the second postpartum year. Behavioural interventions should continue to be prioritized in postpartum women with GDM to optimize this slim window of opportunity for T2D prevention.