Matrix stiffening and associated mechanical stress have been linked to disease and cancer development in multiple tissues. In the liver, cirrhosis, characterized by architectural rearrangements and an up to ten times increase in liver stiffness, is the most significant risk factor for hepatocellular carcinoma development. Patients with non-alcoholic fatty liver disease, typified by lipid-droplet-filled hepatocytes, can, however, develop cancer in non-cirrhotic, and relatively soft tissue. Here, we used primary human hepatocytes to show that lipid droplets are intracellular mechanical stressors with similar effects to tissue stiffening, including hepatocyte dedifferentiation. Specifically, we demonstrate that lipid droplets deform the nucleus, that expression of the hepatocyte transcription factor hepatocyte nuclear factor 4α decreases in proportion to the magnitude of lipid-droplet mediated nuclear deformation, that lipid droplets disrupt the cytoskeleton and resist contractility, preventing cells from properly adapting to stiffer environments, and that modulating contractility rescues hepatocyte differentiation. Mathematical modelling of lipid droplets as spherical inclusions that can have mechanical interactions with other cellular components generated results consistent with our experiments, further supporting the idea that these changes are due to mechanical stress. Taken as a whole, our data show that lipid droplets, and potentially other cytoplasmic inclusions, are intracellular sources of mechanical stress and that nuclear membrane tension may serve to integrate cell responses to combined internal and external stresses.