The outbreak of coronavirus disease 2019 (COVID-19) caused by the betacoronavirus SARS-CoV-2 is now a worldwide challenge for healthcare systems. Although the leading cause of mortality in patients with COVID-19 is hypoxic respiratory failure due to viral pneumonia and acute respiratory distress syndrome, accumulating evidence has shown that the risk of thromboembolism is substantially high in patients with severe COVID-19 and that a thromboembolic event is another major complication contributing to the high morbidity and mortality in patients with COVID-19. Endothelial dysfunction is emerging as one of the main contributors to the pathogenesis of thromboembolic events in COVID-19. Endothelial dysfunction is usually referred to as reduced nitric oxide bioavailability. However, failures of the endothelium to control coagulation, inflammation, or permeability are also instances of endothelial dysfunction. Recent studies have indicated the possibility that SARS-CoV-2 can directly infect endothelial cells via the angiotensin-converting enzyme 2 pathway and that endothelial dysfunction caused by direct virus infection of endothelial cells may contribute to thrombotic complications and severe disease outcomes in patients with COVID-19. In this review, we summarize the current understanding of relationships between SARS-CoV-2 infection, endothelial dysfunction, and pulmonary and extrapulmonary complications in patients with COVID-19.