The oxygen evolution reaction (OER) constrains the efficiency of water splitting. The catalytic activity of electrocatalysts is mostly determined by the electronic structure, which is expressed as the electron transfer property and the reactant adsorption–desorption capacity. Ferromagnetic electrocatalysts exhibit promising applications in OER. However, an external magnetic field is indispensable for the electron spin polarization of ferromagnetic materials. Here, Ni-Fe-Mo ternary alloy nanowire electrocatalysts were prepared via a magnetic field-assisted self-assembly method in an aqueous-solution system at a mild temperature (65 °C). These Ni-Fe-Mo ternary alloy electrodes feature a spin polarization-dependent OER catalytic performance, which is attributed to ferromagnetic regulation. Ni_0.8Fe_0.15Mo_0.05 possesses the maximum ferromagnetism compared to other electrodes (Ni_0.8Mo_0.2 and Ni_0.8Fe_0.2) and improved substantially OER activity. The regulated OER activity is assigned to the favorable adsorption of oxygen-containing intermediates (OH*) due to Ni-Fe-Mo composition-dependent, and the accelerated kinetics of OER with enduring spin polarization. The Ni-Fe-Mo ternary alloy nanowires with higher magnetic properties contribute to in situ spin polarization at the surface. This magnetic field-assisted synthesis approach provides a new strategy to realize electrodes with enduring spin polarized.