Low-cost non-invasive diagnostic tools for staging the progression of non-alcoholic chronic liver failure from fatty liver disease to steatohepatitis are unavailable. Here, we describe the development and performance of a portable single-sided magnetic-resonance sensor for grading liver steatosis and fibrosis using diffusion-weighted multicomponent T2 relaxometry. In a diet-induced mouse model of non-alcoholic fatty liver disease, the sensor achieved overall accuracies of 92% (Cohen's kappa, κ = 0.89) and 86% (κ = 0.78) in the ex vivo grading of steatosis and fibrosis, respectively. Localization of the measurements in living mice through frequency-dependent spatial encoding led to an overall accuracy of 87% (κ = 0.81) for the grading of steatosis. In human liver samples, the sensor graded steatosis with an overall accuracy of 93% (κ = 0.88). The use of T2 relaxometry as a sensitive measure in fully automated low-cost magnetic-resonance devices at the point of care would alleviate the accessibility and cost limits of magnetic-resonance imaging for diagnosing liver disease and assessing liver health before liver transplantation.