Background The long‐term impact of weight gain (WG) on cardiovascular outcomes among patients with atrial fibrillation (AF) is unclear. Methods and Results We studied 62 871 (mean age, 72±12, 43% women) adult patients with AF evaluated at the University of Pittsburgh Medical Center between January 1, 2010, and May 13, 2021. Serial body mass index, risk factors, comorbidities, and subsequent death and hospitalization were ascertained and stratified according to percentage WG (≥0% to <5%, ≥5% to <10%, and ≥10%). Over 4.9±3.19 years of follow‐up, 27 114 (43%) patients gained weight (61%, ≥0% to <5%; 23%, ≥5% to <10%; 16%, ≥10%). Patients with progressive WG were incrementally younger ( P <0.001) women (40%, 42%, and 47%) with lower median household income ( P =0.002) and active smoking (8%, 13% and 13%), and they were less likely to be on a non–vitamin K oral anticoagulant (39%, 37%, and 32%). WG was incrementally associated with a significant increase in risk of hospitalization for AF (≥10% WG; hazard ratio [HR], 1.2 [95% CI, 1.2–1.3]; P <0.0001), heart failure (≥10% WG; HR, 1.44 [95% CI, 1.3–1.6]; P <0.001; ≥5% to <10% WG; HR, 1.17 [95% CI, 1.1–1.2]; P <0.001), myocardial infarction (≥10% WG; HR, 1.2 [95% CI, 1.3–1.6]; P <0.001) and all‐cause stroke (4.2%, 4.3%, and 5.6%) despite significantly lower mean CHADS ₂ Vasc score (2.9±1.7, 2.7±1.6, and 2.7±1.7). Patients with more WG were significantly more likely to receive cardiac and electrophysiologic interventions. Conclusions Among patients with AF, WG is incrementally associated with increased hospitalization for cardiovascular causes, particularly heart failure, stroke, myocardial infarction, and AF.