The Transantarctic Mountains (TAMs) are a ~4,000 km long mountain range, with elevations up to 4,500 m, which separate East and West Antarctica. Given the lack of compressional structures in the TAMs, the origin for these mountains is unclear, and many possible uplift mechanisms have been suggested. The formation of the Wilkes Subglacial Basin (WSB), which is situated inland and parallel to the TAMs, has also been widely debated. A key characteristic to distinguish between different origin models for the TAMs and the WSB is the thickness of the crust beneath these areas. A new 15-station seismic array deployed in the northern TAMs, called the Transantarctic Mountains Northern Network (TAMNNET), as well as 5 stations operated by the Korean Polar Research Institute (KOPRI), are used to investigate the crustal structure beneath a previously unexplored portion of the TAMs and the WSB. Data from the combined TAMNNET and KOPRI networks are analyzed using S-wave receiver functions (SRFs) to estimate the crustal thicknesses. Using both the timing of the conversion from the crust-mantle interface obtained with the SRFs and Rayleigh wave phase velocities, a grid search procedure is used to determine the crustal thickness and velocity beneath each station. Results indicate that the crust is 12-27 km thick near the Ross Sea coast, increasing to a maximum thickness of ~47 km beneath some portions of the TAMs. Further inland, beneath the East Antarctic craton and the WSB, the crust has an average thickness of ~42 km. Average crustal S-wave velocities range from 3.3-3.8 km/s, with the slowest velocities near the coast. These results support a flexural origin model, which jointly explains the uplift of the TAMs and the down-warp of the WSB. Small variations in the crustal thickness may contribute to locally high topography, but crustal isostasy does not appear to play a major role in the overall support of the TAMs.