Rational design of noble-metal-free electrocatalysts with excellent performance for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is critical for next-generation industrial applications of water electrolysis. Here, a simple and robust preparation method of three-dimensional (3D) nanostructured catalysts made of abundant metals is presented. The 3D hydrangea-like microspheres made of nickel-vanadium double hydroxide nanosheets are first prepared on the Ni-Co foam (NCF) followed by the hydroxides exchange with (MoS4)2- ions to form Chevrel-phase Ni-V-Mo sulfide. Benefiting from the 3D holey nanostructures with a large surface area, low adsorption free energy values, and fast electronic transport, the overpotentials of the optimized Ni8V2(Mo3S4)11/NCF catalyst for HER and OER at a current density 10 mA cm-2 are as low as 129 and 330 mV, respectively. The amounts of H2 and O2 generated at a current density of 10 mA cm-2 are about 517 and 342 μmol h-1, which is very competitive with most advanced research results reported for non-noble-metal electrodes in alkaline medium. The Chevrel-phase chalcogenide also features excellent long-term stability under prolonged HER and OER cycling conditions. Our results suggest that Chevrel-phase materials are promising as low-cost and efficient bifunctional electrocatalysts for overall water splitting in alkaline electrolytes.