Vitamin D is a crucial nutrient with numerous pleiotropic effects on health and various chronic diseases. Its hormonal role is manifested not only by its action on classical target organs involved in calcium homeostasis but also by its effects on numerous other tissues and target organs. Over the past decades, there has been an exponential increase in interest in vitamin D, particularly because vitamin D deficiency is associated with multiple diseases, and there is a global prevalence of vitamin D deficiency. Measuring 25-hydroxyvitamin D [25(OH)D] in the serum serves as a biochemical assessment of vitamin status as it reflects the body's vitamin D stores. According to the guidelines for the prevention, recognition, and treatment of vitamin D deficiency in adults, a concentration of 25(OH)D in the plasma of less than 50 nmol/L is defined as a deficiency, 50-75 nmol/L as an insufficiency, and a concentration greater than of 75 nmol/L reflects an adequate vitamin D level. Vitamin D supplements are commonly used to achieve an appropriate vitamin status in the body. Vitamin D2 and D3 are still the most common forms of vitamin D supplementation. In addition to inadequate synthesis of vitamin D in the skin and insufficient intake through food or supplements, various diseases, conditions, and medications can lead to vitamin D deficiency. As much as 93% of patients with chronic liver disease have insufficient levels of vitamin D, and nearly one-third of them show severe deficiency. Low levels of vitamin D due to limited sunlight exposure are common among patients with chronic diseases and are likely an important cause of vitamin D deficiency in cirrhosis and end-stage liver disease. Other causes of low vitamin D levels may include reduced hepatic hydroxylation, increased extrahepatic uptake of vitamin D in adipose tissue, impaired intestinal absorption, and decreased dietary intake. There are numerous pathophysiological mechanisms underlying vitamin D deficiency in patients with chronic liver diseases. The aim of this review is to describe the role of vitamin D on the onset and progression of chronic liver diseases and to investigate the role of vitamin D supplementation on the outcomes of the most common chronic liver diseases.