The current COVID-19 pandemic needs unconventional therapies to tackle the resulted high morbidity and mortality. Convalescent plasma is one of the therapeutic approaches that might be of benefit. Forty nine early-stage critically-ill COVID-19 patients residing in Respiratory Care Units (RCU) of three hospitals in Baghdad, Iraq, were included: 21 received convalescent plasma while 28, namely control group, did not receive it. Recovery or death, length of stay in hospital, and improvement in the clinical course of the disease were monitored clinically along with laboratory monitoring through SARS-CoV-2 RNA detection via PCR, and SARS-CoV-2 IgG and IgM serological monitoring. Patients who received convalescent plasma showed reduced duration of infection in about 4 days and showed less death rate [1/21 versus 8/28 in control group]. In addition, all the patients who were given convalescent plasma showed high levels of SARS-CoV-2 IgG and IgM three days after plasma transfusion. Plasma from donors with high levels of SARS-CoV-2 IgG and donors with positive SRAS-CoV-2 IgM showed better therapeutic results than other donors. Convalescent plasma therapy is an effective therapy if donors with high level of SARS-Cov2 antibodies are selected and if recipients are at their early stage of critical illness, being no more than three days in RCUs.