Background: To investigate whether engagement in leisure-time physical activity before or during pregnancy is associated with low back pain (LBP) outcomes during pregnancy and postpartum prevalence of LBP in women who reported LBP during pregnancy. Methods: Data from the 2015 Pelotas Birth Cohort Study, were used. Demographic, socioeconomic, and gestational characteristics, as well as physical activity prior to and during pregnancy were recorded at perinatal assessment. LBP outcomes during pregnancy (pain intensity, activity limitation, and care seeking) and postpartum (prevalence of LBP) were collected at the 1-year follow-up. Results: Pain intensity, care seeking, and prevalence of LBP postpartum period were not associated with physical activity either before or during pregnancy. However, women engaged in physical activity during pregnancy and at least for 2 trimesters had lower odds ratio of activity limitation associated with LBP during pregnancy (odds ratio: 0.60; 95% confidence interval, 0.41 to 0.88; odds ratio: 0.20; 95% confidence interval, 0.04 to 0.86, respectively). Conclusion: Meeting the recommended levels of physical activity during pregnancy is associated with less activity limitation related to LBP during pregnancy. However, physical activity levels, either before or during pregnancy, were not associated with pain intensity, care seeking, and postpartum LBP.