Background The efficacy of convalescent plasma (CP) for the treatment of COVID-19 remains unclear. Methods A matched cohort analysis of hospitalized patients with severe COVID-19. The impact of CP treatment on all cause in-hospital mortality was evaluated using univariate and multivariate Cox proportional-hazards models, and the impact of CP treatment on the time to hospital discharge was assessed using a stratified log-rank analysis. Results 64 patients who received CP a median of 7 days after symptom onset were compared to a matched control group of 177 patients. Overall in-hospital mortality was 14.9%. There was no significant difference in the risk of in-hospital mortality between the two groups (adjusted hazard ratio [aHR] 0.93, 95% confidence interval [CI] 0.39 − 2.20). There was also no significant difference in the overall rate of hospital discharge (rate ratio [RR} 1.28, 95% CI 0.91 − 1.81), but a subgroup analysis of patients 65-years-old or greater who received CP demonstrated a significantly increased hospital discharge rate among these patients (RR 1.86, 95% CI 1.03 − 3.36). There was a greater than expected frequency of transfusion reactions in the CP group (2.8% reaction rate observed per unit transfused). Conclusions The use of CP in this study was a safe treatment for COVID-19. There was no overall significant reduction of in-hospital mortality or increased rate of hospital discharge associated with the use of CP in this study, although there was a signal for improved outcomes among the elderly. Further adequately powered randomized studies should target this subgroup when assessing the efficacy CP treatment.