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• A novel Ni 43 Mn 32 In 25 Heusler alloy film is deposited on Ni foam by PLD. • The activated NiMnIn/NF possesses overpotentials of 133.4 mV at a current density of –10 mA cm–2 for HER. • Electromagnet is used to realize the electrochemical measurement under in situ magnetic field. • Magnetic field promotes catalytic activity of NiMnIn/NF for HER. [Display omitted] Much effort has been devoted to developing novel electrodes of lower cost and higher efficiency to electrolyze water in scalable applications, which is mainly focused on 3d transition metals or oxides. In this work, Ni 43 Mn 32 In 25 (NiMnIn) Heusler alloy films with highly efficient hydrogen evolution reaction (HER) activity were deposited on porous Ni foam (NF) by pulsed laser deposition. With the synergetic contribution of constituent elements, the as-prepared NiMnIn films exhibited excellent performance with a low overpotential of 189.4 mV in the initial state and 133.4 mV after activation (at a current density of −10 mA cm−2) for HER in alkaline medium. Magnetic measurements have confirmed the ferromagnetic nature of NiMnIn films at room temperature, and the HER activity can be significantly improved by applying a magnetic field. The current density of NiMnIn/NF could be increased by 10% and 7% respectively, at a constant overpotential of 275 mV by applying a magnetic field of 8 kOe perpendicular and parallel to NF. This work suggests that Heusler alloys with various 3d transition metal constituents can be a potential efficient HER active electrode in water splitting, which has the magnetic field sensitivity for applications in magnetoelectrochemistry. [ABSTRACT FROM AUTHOR]