Projections of Antarctica's sea-level contribution depend on future changes in surface mass balance (SMB), yet it remains uncertain whether climate change has already impacted SMB on the East Antarctic Plateau, given diverging trends in prior studies. Using ∼3,000 km of airborne radar data from western Dronning Maud Land (DML), we reconstructed SMB over the past ∼800 years (1209–2024 C.E.) and found stable centennial averages before 1977, followed by a 21% increase in recent decades. This increase is spatially coherent despite strong small-scale variability driven by topography and wind redistribution, which can bias upscaling of firn core records. Integrating radar and firn core data at ∼5x5 km² scales reduces this bias. Our results show an increase in SMB in western DML over the last five decades. If sustained, it could help mitigate sea-level rise.