In addition to catalytic activity, intrinsic stability, tight immobilization on a suitable electrode surface, and sufficient electronic conductivity are fundamental prerequisites for the long‐term operation of particle‐ and especially powder‐based electrocatalysts. We present a novel approach to concurrently address these challenges by using the unique properties of polybenzoxazine (pBO) polymers, namely near‐zero shrinkage and high residual‐char yield even after pyrolysis at high temperatures. Pyrolysis of a nanocubic prussian blue analogue precursor (K_mMn_x[Co(CN)₆]_y⋅n H₂O) embedded in a bisphenol A and aniline‐based pBO led to the formation of a N‐doped carbon matrix modified with Mn_xCo_yO_z nanocubes. The obtained electrocatalyst exhibits high efficiency toward the oxygen evolution reaction (OER) and more importantly a stable performance for at least 65 h.