Background: Stroke significantly increases morbidity and mortality in patients receiving extracorporeal membrane oxygenation (ECMO). This study evaluates the prognostic impact of stroke subtypes, acute ischemic stroke (AIS) and hemorrhagic stroke (HS), and neurologic injury severity in a contemporary adult population. Methods: We conducted a retrospective cohort study using the TriNetX federated electronic health record network, including adult patients who underwent ECMO between 1 October 2015 and 31 December 2025. Stroke was defined as a first-instance diagnosis of AIS, HS, or unspecified cerebrovascular event occurring within 24 h of ECMO cannulation during the index hospitalization. Propensity score matching (1:1 nearest neighbor) was performed to balance baseline demographics, comorbidities, anticoagulant use, and ECMO modality between the stroke and non-stroke cohorts. Primary outcomes included all-cause mortality at 30 days, 90 days, and 1 year. Secondary outcomes included cardiac arrest, seizures, palliative care utilization, and hospital readmission. Kaplan–Meier survival analysis and multivariable Cox proportional hazards modeling were performed. Results: Among 18,981 ECMO patients, 1481 (7.8%) developed a stroke within 24 h of ECMO cannulation, including 814 AIS (54.9%), 454 HS (30.6%), and 213 unspecified cerebrovascular events (14.4%). After propensity score matching, stroke was associated with significantly higher all-cause mortality at 30 days (RR 1.16), 90 days (RR 1.18), and 1 year (RR 1.18), all p < 0.05. Stroke was also associated with higher rates of cardiac arrest, seizures, hospital readmission, and palliative care utilization (all p < 0.001). AIS was associated with significantly lower mortality than HS at 30 days, 90 days, and 1 year (all p < 0.0001). In multivariable Cox regression, only HS was independently associated with increased 30-day mortality compared with no stroke. Markers of neurologic injury severity, including cerebral edema, brain compression, and coma, were among the strongest independent predictors of mortality. Conclusions: Stroke occurring early after ECMO cannulation is associated with substantially worse short- and long-term survival, with hemorrhagic subtype and markers of neurologic injury severity driving the strongest prognostic signals. These findings support early stroke recognition and subtype-informed prognostic discussions in ECMO patients.