The Transantarctic Mountains (TAMs) are the largest noncollisional mountain range on Earth. Their origin, as well as the origin of the Wilkes Subglacial Basin (WSB) along the inland side of the TAMs, has been widely debated, and a key constraint to distinguish between competing models is the underlying crustal structure. Previous investigations have examined this structure but have primarily focused on a small region of the central TAMs near Ross Island, providing little along-strike constraint. In this study, we use data from the new Transantarctic Mountains Northern Network and from five stations operated by the Korea Polar Research Institute to investigate the crustal structure beneath a previously unexplored portion of the TAMs. Using S wave receiver functions and Rayleigh wave phase velocities, crustal thickness and average crustal shear velocity ((V)overbar(s)) are resolved within 4km and 0.1km/s, respectively. The crust thickens from similar to 20km near the Ross Sea coast to similar to 46km beneath the northern TAMs, which is somewhat thicker than that imaged in previous studies beneath the central TAMs. The crust thins to similar to 41km beneath the WSB. (V)overbar(s) ranges from similar to 3.1-3.9km/s, with slower velocities near the coast. Our findings are consistent with a flexural origin for the TAMs and WSB, where these features result from broad flexure of the East Antarctic lithosphere and uplift along its western edge due to thermal conduction from hotter mantle beneath West Antarctica. Locally, thicker crust may explain the similar to 1km of additional topography in the northern TAMs compared to the central TAMs.