The development of a low cost and efficient oxygen evolution reaction (OER) catalyst has paramount importance to meet the future sustainable energy demand. Nature's photosynthetic machinery deploy manganese-based complex in the photosystem II to oxidize water. Inspired by nature, herein, we synthesized a high performing manganese-based OER catalyst using an electrochemically active and iron-rich bacterium, Geobacter sulfurreducens. The as-synthesized biohybrid catalyst (amorphous Geobacter-Mn2O3) produced a current density of 10 mA cm-2at an overpotential of 290 ± 9 mV versus a reversible hydrogen electrode with a low Tafel slope of 59 mV dec-1. The catalyst exhibited remarkable stability, evidenced through a long-term chronopotentiometry experiment. Multiple evidence showed that G. sulfurreducens contributed OER active elements (iron and phosphorus) to the biohybrid catalyst, and the as-synthesized Geobacter-Mn2O3is amorphous. The amorphous structure of the biohybrid catalyst provided a large electrochemically active surface area and excess catalytic sites for the OER catalysis. In addition, Mn3+present in the biohybrid catalyst is believed to be the precursor for oxygen evolution. The OER activity of the biohybrid catalyst outperformed commercial-Mn2O3, commercial-IrO2and most of the benchmark precious OER catalysts, thus supporting its suitability for large-scale applications. The proposed green approach to synthesize a biohybrid catalyst paves a new avenue to develop robust and cost-effective electrocatalysts for energy-related applications.