Background There is still a lack of consensus on the efficacy of convalescent plasma (CP) treatment in COVID‐19 patients. We performed a systematic review and meta‐analysis to investigate the efficacy of CP vs standard treatment/non‐CP on clinical outcomes in COVID‐19 patients. Methods Cochrane Library, PubMed, EMBASE and ClinicalTrials.gov were searched from December 2019 to 16 July 2021, for data from clinical trials and observational studies. The primary outcome was all‐cause mortality. Risk estimates were pooled using a random‐effect model. Risk of bias was assessed by Cochrane Risk of Bias tool for clinical trials and Newcastle‐Ottawa Scale for observational studies. Results In total, 18 peer‐reviewed clinical trials, 3 preprints and 26 observational studies met the inclusion criteria. In the meta‐analysis of 18 peer‐reviewed trials, CP use had a 31% reduced risk of all‐cause mortality compared with standard treatment use (pooled risk ratio [RR] = 0.69, 95% confidence interval [CI]: 0.56‐0.86, P = .001, I 2 = 50.1%). Based on severity and region, CP treatment significantly reduced risk of all‐cause mortality in patients with severe and critical disease and studies conducted in Asia, pooled RR = 0.61, 95% CI: 0.47‐0.81, P = .001, I 2 = 0.0%; pooled RR = 0.67, 95% CI: 0.49‐0.92, P = .013, I 2 = 0.0%; and pooled RR = 0.62, 95% CI: 0.48‐0.80, P < .001, I 2 = 20.3%, respectively. The meta‐analysis of observational studies showed the similar results to the clinical trials. Conclusions Convalescent plasma use was associated with reduced risk of all‐cause mortality in severe or critical COVID‐19 patients. However, the findings were limited with a moderate degree of heterogeneity. Further studies with well‐designed and larger sample size are needed.