Introduction: Cardiopulmonary resuscitation with mechanical devices (MCPR) was developed to provide high-quality cardiopulmonary resuscitation (CPR) for patients with cardiac arrest. However, the effect of this procedure on treatment outcomes remains controversial. Nevertheless, during the coronavirus disease-19 (COVID-19) pandemic, in-hospital MCPR gained attention, owing to its advantages such as saving medical staff and preventing infection. This study compared the treatment outcomes of in-hospital MCPR and manual CPR for out-of-hospital cardiac arrest (OHCA) patients during the COVID-19 pandemic. Materials and Methods: This retrospective nationwide population-based study was conducted in South Korea. Data were collected from the Out-of-Hospital Cardiac Arrest surveillance database managed by the Korea Disease Control and Prevention Agency. We included adult OHCA patients transported by emergency medical services from 2016 to 2021. The study compared outcomes during the COVID-19 pandemic years (2020–2021) with the preceding non-pandemic years (2018–2019). The primary outcome was survival to hospital discharge, and the secondary outcomes were good neurological outcome and sustained return of spontaneous circulation (ROSC). Results: The entire study included 72,050 patients with OHCA and, in the multivariable analyses, MCPR was associated with lower survival rates compared to manual CPR (AOR 0.63; 95% CI 0.51–0.77; p < 0.001). Interestingly, during the COVID-19 pandemic, while MCPR use increased, the survival rate did not differ significantly between the MCPR and manual-CPR groups. Conclusion: Our study findings suggest that while MCPR may offer potential benefits, such as decreased infection risk for healthcare workers, it did not demonstrate superior outcomes compared to manual CPR in our study population.