Published data have shown that physical activity (PA) has a positive role on the primary prevention of breast cancer risk. However, the role of PA on breast cancer outcome has been controversial with inconsistent data. The lack of a meta-analysis that addresses that issue prompted the current report. A comprehensive literature search identified eight studies, of which two studies were excluded. The remaining six studies (12,108 patients with breast cancer) were included in this meta-analysis. Pre-diagnosis PA reduced all causes mortality by 18% but had no effect on breast cancer deaths. Post-diagnosis PA reduced breast cancer deaths by 34% (HR=0.66, 95% CI, 0.57-0.77, P<0.00001), all causes mortality by 41% (HR=0.59, 95% CI, 0.53-0.65, P<0.00001), and disease recurrence by 24% (HR=0.76, 95% CI, 0.66-0.87, P=0.00001). Breast cancer mortality was reduced by pre-diagnosis PA in women with body mass index (BMI)<25 kg/m2, while post-diagnosis PA reduced that risk among those with BMI≥25 kg/m2. On the other hand, post-diagnosis PA reduced all causes mortality regardless of the BMI. The analysis showed that post-diagnosis PA reduced breast cancer deaths (HR=0.50, 95% CI, 0.34-0.74, P=0.0005), and all causes mortality (HR=0.36, 95% CI, 0.12-1.03, P=0.06) among patients with estrogen receptor (ER)-positive tumor, while women with ER-negative disease showed no gain. The current meta-analysis provides evidence for an inverse relationship between PA and mortality in patients with breast cancer and supports the notion that appropriate PA should be embraced by breast cancer survivors.