Non-alcoholic fatty liver disease (NAFLD) and alcohol-related liver disease (ArLD) constitute the primary forms of chronic liver disease, and their incidence is progressively increasing with changes in lifestyle habits. Earlier studies have documented a correlation between the occurrence and development of prevalent mental disorders and fatty liver. To investigate the correlation between fatty liver and mental disorders, thus necessitating the implementation of a mendelian randomization (MR) study to elucidate this association. Data on NAFLD and ArLD were retrieved from the genome-wide association studies catalog, while information on mental disorders, including Alzheimer's disease, schizophrenia, anxiety disorder, attention deficit hyperactivity disorder (ADHD), bipolar disorder, major depressive disorder, multiple personality disorder, obsessive-compulsive disorder (OCD), post-traumatic stress disorder (PTSD), and schizophrenia was acquired from the psychiatric genomics consortium. A two-sample MR method was applied to investigate mediators in significant associations. After excluding weak instrumental variables, a causal relationship was identified between fatty liver disease and the occurrence and development of some psychiatric disorders. Specifically, the findings indicated that ArLD was associated with a significantly elevated risk of developing ADHD (OR: 5.81, 95%CI: 5.59-6.03, < 0.01), bipolar disorder (OR: 5.73, 95%CI: 5.42-6.05, = 0.03), OCD (OR: 6.42, 95%CI: 5.60-7.36, < 0.01), and PTSD (OR: 5.66, 95%CI: 5.33-6.01, < 0.01). Meanwhile, NAFLD significantly increased the risk of developing bipolar disorder (OR: 55.08, 95%CI: 3.59-845.51, < 0.01), OCD (OR: 61.50, 95%CI: 6.69-565.45, < 0.01), and PTSD (OR: 52.09, 95%CI: 4.24-639.32, < 0.01). Associations were found between genetic predisposition to fatty liver disease and an increased risk of a broad range of psychiatric disorders, namely bipolar disorder, OCD, and PTSD, highlighting the significance of preventive measures against psychiatric disorders in patients with fatty liver disease.