Metabolic dysfunction-associated steatotic liver disease (MASLD) featuring hepatic steatosis and insulin dysregulation is becoming a common cause of chronic hepatic diseases. Although the involvement of endocrine disruption in the onset and progression of MASLD is thought to be critical, there are limited effective animal models reflecting hyperinsulinemia and hepatic steatosis. Here, we propose a MASLD mouse model that combines neuropeptide effects and dietary nutrition. We employed chronic overexpression of the gene encoding neurosecretory protein GL (NPGL) in the hypothalamus of ICR mice under a low-fat/medium-sucrose diet (LFMSD). Npgl overexpression promoted fat accumulation in the white adipose tissues in 2 weeks. Basal insulin levels were increased and pancreatic islets expanded following Npgl overexpression. Histological and molecular biological approaches revealed that Npgl overexpression enhanced de novo lipogenesis, leading to hepatic steatosis. Nine-week overexpression of Npgl exacerbated obesity and hyperinsulinemia, resulting in hyperglycemia. Moreover, prolonged Npgl overexpression aggravated fat accumulation in the liver with a change in the lipid metabolic pathway. These findings suggest that Npgl overexpression readily leads to obesity with hyperinsulinemia and hepatic steatosis in ICR mice under an LFMSD.