Objectives The purpose of this study was to quantify the magnitude of association between incremental increases in body mass index (BMI) and the development of incident, post-operative, and post-ablation atrial fibrillation (AF). Background Obesity has been estimated to account for one-fifth of all AF and approximately 60% of recent increases in population AF incidence. From a public health perspective, obesity, therefore, is a modifiable risk factor that could be profitably targeted. Methods A systematic review and meta-analysis was conducted. Medline and EMBASE databases were searched for observational studies reporting data on the association between obesity and incident, post-operative, and post-ablation AF. Studies were included if they reported or provided data allowing calculation of risk estimates. Results Data from 51 studies including 626,603 individuals contributed to this analysis. There were 29% (odds ratio [OR]: 1.29, 95% confidence interval [CI]: 1.23 to 1.36) and 19% (OR: 1.19, 95% CI: 1.13 to 1.26) greater excess risks of incident AF for every 5-U BMI increase in cohort and case-control studies, respectively. Similarly, there were 10% (OR: 1.10, 95% CI: 1.04 to 1.17) and 13% (OR: 1.13, 95% CI: 1.06 to 1.22) greater excess risks of post-operative and post-ablation AF for every 5-U increase in BMI, respectively. Conclusions Incremental increases in BMI are associated with a significant excess risk of AF in different clinical settings. For every 5-U increase in BMI, there were 10% to 29% greater excess risks of incident, post-operative, and post-ablation AF. By providing a comprehensive and reliable quantification of the relationship between incremental increases in obesity and AF across different clinical settings, our findings highlight the potential for even moderate reductions in population body mass indexes to have a significant effect in mitigating the rising burden of AF.