BACKGROUND: The coexistence of persistent atrial fibrillation (AF) and heart failure with reduced left ventricular ejection fraction is associated with greater morbidity and death than either condition alone. Catheter ablation improves outcomes in selected patients, yet results in persistent AF remain unsatisfactory. Convergent hybrid ablation may offer more durable rhythm control by integrating epicardial and endocardial techniques to achieve homogeneous, transmural pulmonary vein and posterior wall isolation. However, randomized data comparing ablation strategies in patients with reduced left ventricular ejection fraction are lacking, leaving a critical evidence gap. METHODS: HALT AF (Hybrid Ablation for Atrial Fibrillation With Heart Failure) is an investigator-initiated, multicenter, prospective, open-label, randomized controlled trial with blinded outcome assessment. A total of 120 patients with nonparoxysmal AF, left ventricular ejection fraction <50%, and at least moderate left atrial dilatation undergoing first-time ablation will be randomized 1:1 to hybrid ablation or catheter ablation. All patients will receive preablation guideline-directed optimization and undergo strategically equivalent ablation (pulmonary vein isolation plus posterior wall isolation). The primary efficacy end point is freedom from recurrent arrhythmia >30 seconds at 12 months and off class I/III antiarrhythmic drugs, excluding a 3-month blanking period. The primary safety end point is major adverse cardiovascular events within 30 days. Secondary end points assess cardiac remodeling, biomarkers, symptoms, and quality of life. CONCLUSIONS: HALT AF will be the first randomized trial to compare convergent hybrid ablation and catheter ablation in patients with persistent AF and reduced left ventricular function. By enrolling only patients with reduced left ventricular ejection fraction and dilated atria and by equating lesion sets, HALT AF is designed to provide critical evidence to inform rhythm-control strategies and guideline recommendations in this high-risk, underrepresented population. REGISTRATION: URL: https://www.clinicaltrials.gov; Unique identifier: NCT05411614.