Fluvial valley networks in mountain ranges record the interactions between climate, tectonics, and lithology. While drainage network analysis has transformed our understanding of these interactions in subaerial settings, the landscape evolution of ice-covered orogens is poorly known. The Gamburtsev Subglacial Mountains are a ~600 km-long mountain range situated beneath the East Antarctic Ice Sheet. These mountains were an important nucleation site for the ice sheet approximately 34 million years ago and are now buried beneath ~2 km of ice. Airborne radar surveying has revealed that the Gamburtsevs are characterised by a rugged, incised landscape, but their geological structure and uplift history remain enigmatic. Here we use a compilation of radar survey data to extract and quantify valley longitudinal profiles from the Gamburtsevs and in turn infer details of their tectonic and geomorphic development. We use 𝜒-mapping and stream power incision modelling to show that the morphology of the valley network is largely consistent with fluvial incision that occurred prior to glaciation. In addition, the spatial distribution of channel steepness indices allows us to confirm the position of major geological boundaries at the edges of the mountains. We also use independent estimates of denudation rates to evaluate competing scenarios for the timing of mountain uplift and valley incision, finding that uplift of the modern Gamburtsevs most likely commenced in the Mesozoic. Regional geomorphic analysis suggests that base level for some Gamburtsev fluvial catchments was set by enclosed interior basins associated with extensional faulting. These depocentres may retain detrital sedimentary material eroded from the Gamburtsevs prior to Antarctic glaciation and are potential targets for future sub-ice drilling campaigns.