Early prognostication post-cardiac arrest can help determine appropriate medical management and help evaluate effectiveness of post-arrest interventions. The Pittsburgh Cardiac Arrest Category (PCAC) severity score is a 4-level illness severity score found to strongly predict patient outcomes in both in- (IHCA) and out-of-hospital cardiac arrests (OHCA). We aimed to validate the PCAC severity score in an external cohort of cardiac arrest patients. Methods: We retrospectively assigned PCAC scores to both IHCA and OHCA patients treated by our hypothermia team from July 1, 2009 to July 1 2016. Our primary outcome was survival to hospital discharge. Secondary outcomes were favorable functional status defined as favorable discharge disposition (home or acute rehabilitation), discharge Cerebral Performance Category (CPC); and discharge modified Rankin Scale (mRS). We tested the association of PCAC and outcomes using a multivariable adjusted logistic regression model. Results: We included 317 subjects in our model. PCAC was strongly associated with survival I Reference; II adjusted odds ratio (OR) 0.20 95% confidence interval (CI) 0.35–0.66, III (OR 0.14 CI 0.3–0.73, p < 0.05); IV (OR 0.05 CI 0.01–0.24, p < 0.01). PCAC was similarly associated with favorable functional outcomes: favorable discharge disposition II (OR 0.12 CI 0.02–0.68), III (OR 0.19 CI 0.05–0.74, p < 0.05) IV (OR 0.05 CI 0.01–0.22, p < 0.01); favorable CPC score II (OR 0.25 CI 0.06–1.03), III (OR 0.14 CI 0.03–0.57, p < 0.01), IV (OR 0.05 CI 0.01–0.20, p < 0.01) and favorable mRS (OR 0.47 CI (0.33–0.68)). Conclusion: Early (<6 h post-arrest) PCAC severity scoring strongly predicts patient outcomes from cardiac arrest in both OHCA and IHCA.