COVID-19 (Coronavirus disease 19) is caused by infection with SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) in the respiratory system and other organ systems. Tissue injuries resulting from viral infection and host hyperinflammatory responses may lead to moderate to severe pneumonia, systemic complications, and even death. While anti-inflammatory agents have been used to treat patients with severe COVID-19, their therapeutic effects are limited. GPR4 (G protein-coupled receptor 4) is a pro-inflammatory receptor expressed on vascular endothelial cells, regulating leukocyte infiltration and inflammatory responses. In this study, we evaluated the effects of a GPR4 antagonist, NE-52-QQ57, in the SARS-CoV-2-infected K18-hACE2 transgenic mouse model. Our results demonstrated that GPR4 antagonist treatment increased the survival rate in this severe COVID-19 mouse model. The inflammatory response, characterized by proinflammatory cytokines and chemokines, was reduced in the GPR4 antagonist group compared with the vehicle group. Additionally, both SARS-CoV-2 RNA copy numbers and infectious viral titers in the mouse lung were decreased in the GPR4 antagonist group. The percentage of SARS-CoV-2 antigen-positive mouse brains was also decreased in the GPR4 antagonist group compared to the vehicle group. Furthermore, the GPR4 antagonist inhibited SARS-CoV-2 propagation in Vero E6 and Caco-2 cells. Together, these results suggest that GPR4 antagonism may be explored as a novel approach for the treatment of COVID-19 and other similar viral diseases.