Assessing the impact of glaciations on topography and the co-evolution of ice-sheet dynamics requires a thorough understanding of the factors that control fjord morphology. We investigate the role of lithology on glacial valley form using topographic analyses and numerical landscape evolution models. We measure fjord depths and widths from East Central Greenland (68°N–75°N), and find a control of lithology on fjord width, with wider fjords in softer rocks (i.e., sedimentary rocks). This dependency of fjord width to bedrock properties is predicted by a quarrying erosion law, but not by an abrasion one, when considering results from a simple two-dimensional model and a more detailed three-dimensional ice flow model (iSOSIA). Our analyses and numerical results reveal a potential control of lithology on the width of glacial valleys with glacial quarrying as a plausible responsible mechanism.