PURPOSE: The purpose of this umbrella review was to synthesize the evidence from systematic reviews on the benefits and harms of exercise therapy and physical activity (PA) for the secondary prevention and management of low back pain (LBP). METHODS: An umbrella review was conducted to evaluate the effectiveness of exercise therapy and PA in the management and secondary prevention of LBP. A systematic search was performed in MEDLINE, CINAHL, Scopus, Web of Science, Cochrane Database of Systematic Reviews, and Physiotherapy Evidence Database (PEDro), including reference lists of relevant reviews, covering studies published between January 1, 2010 and May 20, 2024. Eligible studies were systematic reviews of randomized controlled trials and observational studies, with or without meta-analyses. The primary outcome for secondary prevention was LBP recurrence, while for management, primary outcomes included pain intensity and disability, with adverse events as secondary outcomes. Data were extracted across immediate, short-term, intermediate, and long-term follow-up periods. The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) framework was used to assess the certainty of evidence, and the Assessment of Multiple Systematic Reviews tool (AMSTAR) tool was applied by 2 independent reviewers (JC, QL, and/or DXMW) to evaluate the quality of the included reviews. The study was prospectively registered on the Open Science Framework (OSF). RESULTS: A total of 70 systematic reviews were included, 43 with meta-analyses, 7 with network meta-analyses, and 20 without meta-analyses. Six (out of 10) reviews with meta-analyses for secondary prevention indicated a small benefit from general exercises and leisure-time PA (low-to-moderate certainty). For LBP management, 35 (out of 36) reviews reported that exercise therapies such as Pilates, motor control, mixed exercise, Tai Chi, water-based exercises, and yoga showed small beneficial effects on pain and disability compared to minimal intervention mainly in the short-term (low-to-moderate certainty). Seven network meta-analyses favored motor control and Pilates over other forms of exercise to reduce pain (low certainty). Adverse events were reported in less than 31% of the reviews, predominantly involving post-exercise soreness and temporary increases in pain, mainly in yoga-related studies. Adverse events were considered minor, and no serious adverse events were reported. CONCLUSION: There is low-to-moderate certainty that exercise therapy and leisure-time PA are beneficial for improving pain and preventing the recurrence of LBP. However, evidence on the potential harms of these interventions is limited, and adverse events related to exercise and PA remain under-investigated.