Lumbopelvic pain (LBPP) affects 45% to 81% of pregnant women, and 25% to 43% of these women report persistent LBPP beyond 3 months after giving birth. The objective of this study was to investigate the association of physical activity, weight status, anxiety, and evolution of LBPP symptoms in postpartum women. This was a prospective observational cohort study with 3 time-point assessments: baseline (T0), 3 months (T3), and 6 months (T6). Women with persistent LBPP 3 to 12 months after delivery were recruited. At each time point, pain disability was assessed with the Pelvic Girdle Questionnaire and the Oswestry Disability Index (ODI), physical activity with Fitbit Flex monitors, and anxiety with the French-Canadian version of the State-Trait Anxiety Inventory. Weight was recorded using a standardized method. Pain intensity (numerical rating scale, 0-100) and frequency were assessed using a standardized text message on a weekly basis throughout the study. Thirty-two women were included (time postpartum: 6.6 ± 2.0 months; maternal age: 28.3 ± 3.8 years; body weight: 72.9 ± 19.1 kg), and 27 completed the T6 follow-up. Disability, pain intensity, and pain frequency improved at T6 (P < .001). Participants lost a mean of 1.9 ± 4.5 kg at T6, and this weight loss was correlated with reduction in LBPP intensity (r = 0.479, P = .011) and LBPP frequency (r = 0.386, P = .047), Pelvic Girdle Questionnaire score (r = 0.554, P = .003), and ODI score (r = 0.494, P = .009). Improvement in ODI score at T6 was correlated with the number of inactive minutes at T3 (r = −0.453, P = .026) and T6 (r = −0.457, P = .019), and with daily steps at T6 (r = 0.512, P = .006). Weight loss is associated with positive LBPP symptom evolution beyond 3 months postpartum, and physical activity is associated with reduction in pain disability.