Searching active and cost-effective bifunctional electrocatalysts for overall water splitting is a vital but challenging task towards clean and sustainable energy sources. Here, mixed metal phosphides of Ni2PCoP anchored on N-doped reduced graphene oxide (NiCoP/N-rGO) as efficient and earth-abundant electrocatalysts for water splitting are reported. The large active sites, synergism, and hybridization with N-doped rGO endow NiCoP/N-rGO electrocatalyst with outstanding oxygen evolution reaction activity that is better than benchmark RuO2 in alkaline electrolyte, as well as active hydrogen evolution reaction in acidic, neutral, and alkaline solution. NiCoP/N-rGO has further been employed as both anode and cathode in a two-electrode alkaline water electrolyzer towards overall water splitting, exhibiting advanced electrochemical performances with a low cell voltage of 1.57 V at a current density of 20 mA cm−2. Moreover, the overall water splitting in this two-electrode electrolyzer can be driven by a single-cell AA battery (nominal voltage of 1.5 V), making NiCoP/N-rGO as the promising efficient cost-effective catalysts for water electrolysis.