Abstract Introduction: Observational studies have revealed an association between waist circumference (WC) and atrial fibrillation (AF). However, it is difficult to infer a causal relationship from observational studies because the observed associations could be confounded by unknown risk factors. Therefore, the causal role of WC in AF is unclear. This study was designed to investigate the causal association between WC and AF using a two-sample Mendelian randomization (MR) analysis. Methods: In our two-sample MR analysis, the genetic variation used as an instrumental variable for MR was acquired from a genome-wide association study (GWAS) of WC (42 single nucleotide polymorphisms with a genetic significance of P <5 × 10^–8). The data of WC (from the Genetic Investigation of ANthropometric Traits consortium, containing 232,101 participants) and the data of AF (from the European Bioinformatics Institute database, containing 55,114 AF cases and 482,295 controls) were used to assess the causal role of WC on AF. Three different approaches (inverse variance weighted [IVW], MR–Egger, and weighted median regression) were used to ensure that our results more reliable. Results: All three MR analyses provided evidence of a positive causal association between high WC and AF. High WC was suggested to increase the risk of AF based on the IVW method (odds ratio [OR] = 1.43, 95% confidence interval [CI], 1.30–1.58, P = 2.51 × 10^-13). The results of MR–Egger and weighted median regression exhibited similar trends (MR–Egger OR = 1.40 [95% CI, 1.08–1.81], P = 1.61 × 10^-2; weighted median OR = 1.39 [95% CI, 1.21–1.61], P = 1.62 × 10^-6). MR–Egger intercepts and funnel plots showed no directional pleiotropic effects between high WC and AF. Conclusions: Our findings suggest that greater WC is associated with an increased risk of AF. Taking measures to reduce WC may help prevent the occurrence of AF.