We conducted a prospective single-arm open-label phase II clinical trial assessing the safety and efficacy of convalescent plasma in hospitalized COVID-19 patients. Convalescent plasma with sufficient IgG titer (1:320) obtained from recovered donors was administered to adult patients with either severe or critical COVID-19 illness. Primary outcomes were adverse events in association with plasma administration, and hospital mortality. Secondary outcomes included disease progression, recovery, length of stay, and hospital discharge. Of the 38 patients included in the analysis, 24 (63%) recovered and were discharged, and 14 (37%) died. Patients who received convalescent plasma early in the disease course (severe illness group) as compared to the patients that received convalescent plasma later in disease progression (critical illness group) had significantly lower hospital mortality 13% vs 55% (p<0.02) and shorter mean hospital length of stay 15.4 vs 33 days (p<0.01). One patient experienced a transient transfusion reaction. No other adverse effects of convalescent plasma infusion were observed. Our results suggest that convalescent plasma is safe and has the potential for positive impact on clinical outcomes including recovery and survival if given to patients early in the course of COVID-19 disease.