Abstract The Antarctic–South American subduction zone is among the least explored convergent margins and lacks documented large interplate earthquakes despite ongoing convergence. Here we report the discovery of tectonic tremor along this plate boundary using continuous seismic data. These observations provide the first direct seismic evidence of active deformation along the Antarctic–South American plate interface, suggesting that a portion of accumulated strain may be released aseismically. We document deep tectonic tremor occurring at depths of approximately 30–40 km, where the geometry and downdip termination of the plate interface were previously unconstrained. Tremor migration patterns and modulation by ocean tides further support an origin associated with slow deformation processes on the plate boundary. Our results provide new constraints on strain accommodation and suggest that tectonic tremor can help constrain plate boundary geometry in regions where conventional seismicity provides limited information.