The prevalence of fatty liver disease (FLD) and that of non-alcoholic fatty liver disease (NAFLD) share some risk factors known to exacerbate the course of acute pancreatitis (AP). This meta-analysis aimed to investigate whether FLD or NAFLD carry a higher risk of untoward outcomes in AP. In accordance with PRISMA guidelines, we performed a systematic search in seven medical databases for cohort studies that compared the outcomes of AP for the presence of FLD or NAFLD, and we calculated pooled odds ratio (OR) or weighted mean difference (WMD) with 95% confidence interval (CI). We included 13 articles in our meta-analysis. AP patients with FLD were more likely to die (5.09% vs 1.89%, OR = 3.56, CI = 1.75–7.22), develop severe AP (16.33% vs 7.87%, OR = 2.67, CI = 2.01–3.56), necrotizing pancreatitis (34.83% vs 15.75%, OR = 3.08, CI = 2.44–3.90) and had longer in-hospital stay (10.8 vs 9.2 days, WMD = 1.46, OR = 0.54–2.39). Patients with NAFLD were more likely to have severe AP and longer hospital stay. Both FLD and NAFLD proved to be independent risk factors of a more severe disease course (OR = 3.68, CI = 2.16–6.29 and OR = 3.39, CI = 1.52–7.56 for moderate/ severe vs. mild AP, respectively). FLD and NAFLD worsen the outcomes of AP, which suggests that incorporating FLD or NAFLD into prognostic scoring systems of AP outcomes might improve the prediction of severity and contribute to a more individualized patient care.