Background: The increasing prevalence of type 2 diabetes mellitus (T2DM) and non-alcoholic fatty liver disease (NAFLD) states a serious problem for public health. The introduction of effective methods of treatment and prevention is crucial to avoid complications of these diseases. Among them, we can specify psychological factors that affect everyday life and determine the patient’s attitude towards therapy, and what follows, their compliance in treatment. The literature indicates these connections in various ways; in our study, we extend this view to include a broader perspective of human personality. Objective: We decided to investigate the associations between personality factors and metabolic parameters in patients with NAFLD and T2DM in order to better understand the patient’s approach to the treatment of a chronic disease, such as those mentioned, and to establish the basis for further research implementing psychological interventions in the treatment of NAFLD and T2DM. Methods: One hundred participants with NAFLD and T2DM underwent blood tests and anthropometric measures. Each of them was asked to complete five questionnaires evaluating their personality properties. Results: We revealed that a rise in body mass index is related to a fall in the emotional intelligence factor of utilizing emotions, and a rise in emotional perception. The decrease in task-oriented coping style and a rise in emotion-oriented coping style are associated with a waist-hip ratio increase. The increase in fasting plasma glucose is predicted by a decrease in task-oriented coping style score. A fall in social diversion coping style score is associated with a high-density lipoprotein increase; in turn, a triglycerides increase is connected with a decline in rhythmicity score. Conclusions: The personality factors are in relationship in the management of NAFLD and T2DM. They affect a patient’s approach to treatment, which is very important, because we know lifestyle and dietary interventions are an important part of the treatment of these diseases. The compliance manifests by lifestyle modifications, taking medications regularly, measuring blood glucose, and inspection visits in outpatients’ clinics are a large part of a diabetic’s life. Future studies introducing psychological intervention to improve, e.g., coping styles or rhythmicity are needed to implement new methods of patient management.