Industrially profitable water splitting is one of the great challenges in the development of a viable and sustainable hydrogen economy. Alkaline electrolysers using Earth-abundant catalysts remain the most economically viable route to electrolytic hydrogen, but improved efficiency is desirable. Recently, electron spin polarization was described as a potential way to improve water-splitting catalysis. Here, we report the significant enhancement of alkaline water electrolysis when a moderate magnetic field (≤450 mT) is applied to the anode. Current density increments above 100% (over 100 mA cm⁻²) were found for highly magnetic electrocatalysts, such as the mixed oxide NiZnFe₄O_x. Magnetic enhancement works even for decorated Ni–foam electrodes with very high current densities, improving their intrinsic activity by about 40% to reach over 1 A cm⁻² at low overpotentials. Thanks to its simplicity, our discovery opens opportunities for implementing magnetic enhancement in water splitting.