High energy electron bunches from the laser-driven relativistic magnetic reconnection (MR) has been intensively studied. However, diagnostic methods for identifying such acceleration mechanism remain inadequate. This study utilizes 2.5-dimensional particle-in-cell simulations to explore a diagnostic approach based on electron polarization dynamics governed by the Thomas–Bargmann–Michel–Telegdi equation. The trajectories of electrons accelerated by the MR are confined in the current sheet, where the magnetic field is effectively annihilated. The resulting electron beam exhibits extremely low depolarization, distinguishing it from other accelerated populations and serving as a definitive signature of MR. This diagnostic approach enables more detailed investigations of MR—driven acceleration mechanisms in future studies.