Non-alcoholic fatty liver disease (NAFLD) and subsequent steatohepatitis (NASH) is the most common cause of liver disease and liver transplantation in humans. Affecting millions of patients worldwide, diagnosis relies on a biopsy, not without risk to the patient, and emphasises the need for improved diagnostic measures to determine and monitor disease progression. Despite intensive research, approved pharmacological treatment modalities are few, underlining that animal models with increased translational validity are important to advance preclinical drug development. This study validates the applicability of computed tomography (CT) as a non-invasive diagnostic tool for the assessment of liver steatosis in a guinea pig model of NAFLD/NASH. Guinea pigs with induced NAFLD or NASH were compared to healthy controls at two separate time points: week 16, serving as baseline measure, and week 25 to monitor disease progression over time. The animals were subsequently euthanised, and samples were collected to confirm disease stage. The data showed a strong negative correlation between liver triglycerides and Hounsfield unit (HU) values (R² = 0.8157; p < 0.0001). A significant difference in histopathological scoring and HU values between grade 0 and more advanced stages of steatosis was recorded (p < 0.001), although the degree of liver fibrosis could not be accurately evaluated by differences in HU. In conclusion, the present study validates CT scanning for the determination of hepatic steatosis in guinea pigs, and it strongly supports the technique as a relevant non-invasive diagnostic tool in this species.