Background: Regular physical activity (PA) and healthy body weight have proven benefits on survival in breast cancer (BC) survivors. We aimed to define predictors of long-term PA and weight gain in a representative sample of BC survivors. Methods: Data were analysed from 723 women with BC who participated in both the 2012 and 2015 French National VICAN surveys. Results: Five years after diagnosis, 26.0, 60.6, and 13.4 % of BC survivors reported regular, occasional and no PA, respectively. Moreover, 27.4 % had a weight gain 5 kg. In multinomial logistic regressions, regular and occasional PA were both associated with not having depressive disorders, with higher post-traumatic growth, and with a healthy and stable Body Mass Index. Occasional PA was associated with the use of non-conventional medicine, and regular PA with better mental quality of life and normal arm mobility. Weight gain 5 kg was associated with younger age, heavier body weight at diagnosis, and lymphedema 5 years after diagnosis. Conclusions: Mental well-being is associated with successful long-term patient investment in PA. Psychological support and early management of disease sequelae are needed to help ensure BC survivors engage in and maintain healthy lifestyles.