Background— Recent data suggest that β-blockers are associated with prognostic advantages in heart failure (HF) patients without concomitant atrial fibrillation (AF), but not in HF patients with concomitant AF. We aimed to investigate associations between β-blocker treatment and cardiovascular outcome and mortality in AF patients with and without HF. Methods and Results— Three nationwide registries were used to identify patients with nonvalvular AF patients with or without concomitant HF. Patients were stratified into β-blocker users and β-blocker nonusers, and according to the presence of a HF diagnosis. We followed the patients ≤5 years after baseline. Six different cardiovascular outcomes were investigated, including all-cause mortality and fatal thromboembolic events. Crude event rates were ascertained and propensity-matched Cox regression was used to compare event rates according to β-blocker usage status. A total of 205 174 patients were included, where 39 741 patients had prevalent HF. In the latter subgroup of patients, the 1-year propensity-matched hazard ratio (HR) for all-cause mortality was 0.75 (95% confidence interval, 0.71–0.79; nontreated used as reference). For patients without concomitant HF, the propensity-matched HR for all-cause mortality was 0.78 (95% confidence interval, 0.71–0.76). Conclusions— In this large nationwide cohort study, evidence of a lower mortality with β-blocker therapy in AF patients with concomitant HF was observed. In addition, this association was accompanied with indications that β-blocker treatment is also associated with a better prognosis in AF patients without concomitant HF.