Background: We aimed to determine if the ABO blood types carry different risks of 30-day mortality, acute kidney injury (AKI), and endothelial damage in critically ill patients with sepsis. This was a retrospective cohort study of three independent cohorts of critically ill patients from the United States and Scandinavia consisting of adults with septic shock. We compared the 30-day mortality across the blood types within each cohort and pooled the results in a meta-analysis. We also estimated the incidence of AKI and degree of endothelial damage, as measured by blood concentrations of soluble thrombomodulin and syndecan-1. Results: We included 12,342 patients with severe sepsis. In a pooled analysis blood type B carried a slightly lower risk of 30-day all-cause mortality compared to non-blood type B (adjusted HR 0.88; 95%-CI 0.79–0.98; p = 0.02). There was no difference in the risk of AKI. Soluble thrombomodulin and syndecan-1 concentrations were lower in patients with blood type B and O compared to blood type A, suggesting less endothelial damage. Conclusion: Septic patients with blood type B had less endothelial damage, and a small reduction in mortality. The exposure is, however, unmodifiable.