Background Various ECG criteria for left ventricular hypertrophy (LVH) have been proposed, but their association with clinical outcomes in patients with severe aortic stenosis undergoing transcatheter aortic valve replacement is unknown. We investigated the prevalence of ECG LVH according to different criteria and its prognostic impact on clinical outcomes after transcatheter aortic valve replacement. Methods and Results In this prospective observational cohort, we evaluated 700 patients who underwent transcatheter aortic valve replacement between March 2010 and December 2019. Baseline preprocedural LVH was defined by 3 ECG criteria—Sokolow‐Lyon, Romhilt‐Estes, and Cornell voltage criteria. The primary outcome was major adverse cardiac or cerebrovascular event (MACCE; composite of death, myocardial infarction, stroke, or rehospitalization from cardiovascular cause); the key secondary outcome was all‐cause and cardiovascular mortality. Among 596 eligible patients, the prevalence of LVH was determined as 56.3% by Sokolow‐Lyon, 31.1% by Romhilt‐Estes, and 48.1% by Cornell criteria. Regardless of the criteria, patients with ECG LVH had more severe aortic stenosis hemodynamics and higher left ventricular mass index. After multivariate adjustment, the presence of LVH by the Cornell criteria was significantly associated with lower risks of MACCE (adjusted hazard ratio [HR], 0.68; 95% CI, 0.51–0.91; P =0.009), all‐cause mortality (adjusted HR, 0.55; 95% CI, 0.34–0.90 [ P =0.017]), and cardiovascular mortality (adjusted HR, 0.40; 95% CI, 0.20–0.79 [ P =0.008]). However, this association was absent with the Sokolow‐Lyon and Romhilt‐Estes criteria. Conclusions ECG LVH by Cornell criteria only was significantly associated with lower risks of MACCE and all‐cause or cardiovascular mortality. Registration URL: https://www.clinicaltrials.gov ; Unique identifier: NCT03298178.