Environmental regulations are very strict for selenium requiring its removal from various streams down to <5 ppb. In this context, selenate, Se(VI), that is often encountered in waste waters originating from mining, metallurgical, chemical, and semiconductor industries, imposes particular challenges to its effective elimination due to poor adsorption and reduction. In this work, the effective removal of Se(VI) down to 5 ppb level is described via the use of nano zero-valent iron, nZVI, that acts as a strong reducing agent. Emphasis is given on elucidating the galvanic mechanism of selenate reduction and immobilization on nZVI surface with the view of achieving increased electron efficiency that translates to selectivity against the undesirable excess consumption of nZVI by parasitic hydrogen evolution without sacrificing environmental effectiveness. Through extensive nanoscale surface characterization, the Se uptake mechanism was determined to involve (1) selenate reduction to selenite via reductive adsorption on the hydrous Fe(II)-oxide surface of nZVI and (2) sequential galvanic reduction to elemental selenium through the Se-enriched Fe(0/II/III) oxide layer. It was found the formation of Se0 nanoclusters on nZVI to play a significant role in enhancing the selective reduction of selenium while simultaneously suppressing the parasitic evolution of hydrogen. These findings may lead to further testwork on the design and application of stable nZVI systems yet with high efficiency and effectiveness for reductive elimination of hazardous species of environmental concern.