Background Limited data are available on the clinical impact of healthy lifestyle behaviors on the risk of dementia in patients with new‐onset atrial fibrillation (AF). Here, we aimed to evaluate the association between a combination of healthy lifestyle behaviors and the risk of incident dementia in patients with AF. Methods and Results Using the Korean National Health Insurance database between 2009 and 2016, we identified 199 952 adult patients who were newly diagnosed as AF without dementia. Patients were categorized into 4 groups by healthy lifestyle behavior score (HLS) with 1 point each being assigned for no current smoking, alcohol abstinence, and regular exercise. The HLS 0, 1, 2, and 3 groups included 4.4%, 17.4%, 53.4%, and 24.8% of the patients, respectively. We performed an inverse probability of treatment weighting to balance covariates between HLS groups. The HLS 1, 2, and 3 groups were associated with a lower risk of dementia compared with the HLS 0 group (hazard ratio [HR], 0.769; 95% CI, 0.704–0.842 for HLS 1; HR, 0.770; 95% CI, 0.709–0.836 for HLS 2; and HR, 0.622; 95% CI, 0.569–0.679 for HLS 3). The risk of dementia showed a tendency to decrease with an increase in HLS ( P ‐for‐trend <0.001). Conclusions A clustering of healthy lifestyle behaviors was associated with a significantly lower risk of dementia in patients with new‐onset AF. These findings support the promotion of a healthy lifestyle within an integrated care approach to AF patient management.