Introduction Post-operative atrial fibrillation (POAF) is one of the most common complications following cardiac surgery. However, it is unclear whether there is a relationship between obesity and POAF. We thus assessed all available evidence investigating the association between obesity and POAF, also considering any link between POAF and other post-operative conditions such as mortality, stroke, myocardial infarctions and respiratory complications. Methods Five electronic databases were searched and relevant studies were identified. Data was extracted and meta-analyzed from the identified studies. Results We found that obese patients had significantly higher odds of POAF when compared with non-obese patients (P = 0.006). There was also significant heterogeneity among the identified studies. POAF when compared with no-POAF was associated with an increased risk of stroke (P < 0.0001), 30-day mortality (P = 0.005) and respiratory complications (P < 0.00001). However, we found no significant link between POAF and myocardial infarctions (P = 0.79). Conclusions Our findings suggest that obesity is associated with a moderately higher risk of POAF. While POAF is also associated with an increased incidence of stroke, 30-day mortality and respiratory complications, further studies must be conducted before conclusions can be made about the long-term outcomes.