The clinical benefit of convalescent plasma for COVID-19 patients is still debated. In this systematic review and meta-analysis, we selected 10 randomized clinical trials (RCTs) and 15 non-randomized studies (total number of patients = 22,591) of convalescent plasma treatment and evaluated two different scenarios: 1- disease stage of plasma recipients and 2 – donated plasma antibody titer, considering all-cause mortality at the latest follow-up. Our results show that, when provided at early stages of the disease, convalescent plasma significantly reduced mortality (RR 0.72, p<0.00001), while provided in severe or critical conditions, it did not (RR 0.94, p=0.22). On the other hand, the benefit on mortality was not increased by using plasma with a high antibody titer compared to unselected plasma. This meta-analysis might promote convalescent plasma usage in patients with early stage COVID-19 in further RCTs to maximize its benefit in decreasing mortality, especially in less affluent countries.