The marine‐based portions of the East Antarctic Ice Sheet are currently losing mass at an accelerating rate due to atmospheric and oceanic forcing. Assessing these changes requires understanding long‐term grounding‐zone dynamics preserved in glacial geomorphology, including understudied East Antarctic shelf sectors. We present geophysical evidence for the detailed internal architecture of a giant ∼260 m‐high grounding‐zone wedge (GZW) in Vincennes Bay just offshore the Aurora Subglacial Basin. A bed slope transition from retrograde to prograde likely slowed grounding‐zone retreat, culminating in a stillstand. Prograding internal foresets indicate a single major stabilization event tied to a ∼65 km grounding‐line readvance, probably after the Last Glacial Maximum. The new high‐resolution seismic data allow analyzing the nucleation and the evolution of a GZW in unprecedented detail, thus providing key constraints on grounding‐zone behavior and its sensitivity to local topography and associated subglacial geological variations along ice‐sheet beds. Earth's ice sheets have been losing mass since the Last Glacial Maximum. Specific seafloor structures can be used to reconstruct past ice sheet extent, thereby serving as control points for ice sheet models. Such models are used to predict future ice development with respect to climate change. We present a new high‐resolution geophysical data set from Vincennes Bay, East Antarctica revealing a newly discovered ∼260 m‐high and ∼65 km‐long asymmetric wedge‐shaped structure. This structure is called a grounding‐zone wedge and was formed during a temporary self‐stabilization process that occurs during a general regional ice retreat. This leads to a stillstand, followed by a subsequent readvance of the transition zone between floating and grounded ice. Material transported with the glacier into Vincennes Bay led to front growth toward the sea. The large dimensions of this grounding‐zone wedge suggest a high sedimentary supply and a significant long stabilization period during general ice retreat after the Last Glacial Maximum. High‐resolution images of the internal geometry of the grounding‐zone wedge enables the reconstruction of formation processes of grounding‐zone wedges. Detailed reconstruction of a post‐Last Glacial Maximum grounding‐zone wedge formation based on high‐resolution 2D seismic reflection data Full display of internal geometry reveals initiation of stabilization and subsequent formation of a self‐stabilizing grounding‐zone wedge Prograding sequences built‐up a 260 m‐high and 65 km‐long grounding‐zone wedge in Vincennes Bay Detailed reconstruction of a post‐Last Glacial Maximum grounding‐zone wedge formation based on high‐resolution 2D seismic reflection data Full display of internal geometry reveals initiation of stabilization and subsequent formation of a self‐stabilizing grounding‐zone wedge Prograding sequences built‐up a 260 m‐high and 65 km‐long grounding‐zone wedge in Vincennes Bay