BACKGROUND: Physical activity after cancer diagnosis may reduce mortality. However, systematic evidence for this association for men living with prostate cancer remains limited. METHODS: We searched PubMed, Embase, and CINAHL data bases from start to June 2025. Random-effects meta-analyses estimated summary hazard ratios (HRs) and 95% confidence intervals (CI) for all-cause mortality and prostate-cancer-specific mortality to assess the association between post-diagnosis physical activity, measured in metabolic equivalents of task-hours per week (MET-hr/week), and mortality among prostate cancer survivors. RESULTS: We included ten studies with more than 50,144 participants (one study did not report the number of prostate cancer cases included in the meta-analysis) and 28,044 deaths. Higher levels of post-diagnosis physical activity (≥ 7.5 MET-hr/week) were associated with lower all-cause mortality (HR = 0.69; 95% CI: 0.62-0.77), compared to lower levels (< 7.5 MET-hr/week). Meta-analysis of five studies showed an inverse association between post-diagnosis physical activity and prostate cancer-specific mortality (HR = 0.77; 95% CI: 0.66-0.89). Meta-analysis of four studies showed that moderate-to-vigorous physical activity was inversely associated with mortality (HR = 0.62; 95% CI: 0.51-0.74). CONCLUSION: Higher post-diagnosis physical activity, including activity at higher intensities, was associated with lower all-cause and prostate cancer-specific mortality among men living with prostate cancer. Our findings suggest that physical activity may complement cancer care for prostate cancer patients.