Mg2Ni alloy prepared by vacuum induction melting is rapidly quenched in the presence of an external magnetic field. The effects of magnetic field on the microstructure and electrochemical hydrogen storage behavior of Mg2Ni alloy are well investigated for the first time. X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) studies show that the applied magnetic field results in a preferred orientation growth during the rapid solidification of alloy melt, which induces the generation of columnar crystals. Meanwhile, decreased grain size and increased internal strain are noted for this alloy, as well as the eliminated composition segregation. It is found on the charge–discharge experiments that the as-prepared alloy displays an increased capacity and improved cycle stability compared to the alloys without magnetic field treatment. The potentiodynamic polarization results indicate that the Mg2Ni alloy exhibits relatively high corrosion resistance against the alkaline solution. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) results demonstrate enhanced electrochemical kinetics for the treated Mg2Ni alloy, consistent with the enhanced electrochemical properties.