Fibrosis is a pathological condition that leads to excessive deposition of collagen and increased tissue stiffness. Understanding the mechanobiology of fibrotic tissue necessitates the development of effective in vitro models that recapitulate its properties and structure; however, hydrogels that are currently used for this purpose fail to mimic the filamentous structure and mechanical properties of the fibrotic extracellular matrix (ECM). Here, we report a nanofibrillar hydrogel composed of cellulose nanocrystals and gelatin, which addresses this challenge. By altering the composition of the hydrogel, we mimicked the changes in structure, mechanical properties, and chemistry of fibrotic ECM. Furthermore, we decoupled the variations in hydrogel structure, properties, and ligand concentration. We demonstrate that this biocompatible hydrogel supports the three-dimensional culture of cells relevant to fibrotic diseases. This versatile hydrogel can be used for in vitro studies of fibrosis of different tissues, thus enabling the development of novel treatments for fibrotic diseases.