The electrocatalytic nitrogen reduction reaction (NRR) provides a promising avenue for sustainable and decentralized green ammonia (NH3) synthesis. To promote the NRR, the design and synthesis of efficient electrocatalysts with an elucidated reaction mechanism is critically important. Here, surface hydrogenation‐facilitated NRR is demonstrated to yield NH3 at low overpotentials on oxygen‐deficient In2O3 plates decorated with single atom CdO5 that have a weak N2‐binding capability. Adsorbed *H is calculated to be first produced via the Volmer reaction (H2O + e− → *H + OH−) and then reacts with dissolved N2 to generate *N2H2, which is likely the rate determining step (RDS) of the whole process. Cd atoms and oxygen vacancies in In2O3 jointly enhance the activation of N2 and accelerate the RDS, boosting the NRR. An NH3 production rate of as high as 57.5 µg h−1 mgcat−1 is attained at a mild potential, which is retained to a large extent even after 44 h of continuous polarization. Surface pre‐adsorbed hydrogen is found to facilitate N2 activation to yield NH3 on single atom CdO5 decorated In2O3 plates with oxygen vacancies that have weak N2‐binding strength. An NH3 production rate of up to 57.5 µg h−1 mgcat−1 is achieved at a mild overpotential, which is retained to a large extent even after 44 h of continuous electrolysis.