Industrial alkaline water electrolysis is facing major difficulties in developing inexpensive, abundant and active bifunctional non-noble metal electrocatalysts. Herein, a heterogeneous three-dimensional (3D) FeNi2S4@Mo-doped Ni3S2/NF heterostructure electrocatalyst is synthesized by a controlled two-step hydrothermal method. Based on the unique structural advantages, the number of redox active sites and the conductivity of the heterostructure electrode are improved remarkably resulting the shortening of ion diffusion path, effective penetration of the electrolyte and decrease in equivalent series resistance. The electrode achieves 10 mA cm−2 current density in hydrogen evolution reaction and oxygen evolution reaction at ∼121 and 150 mV overpotential, respectively in alkaline solution. The bifunctional electrochemical performance of the heterostructure is confirmed from the low cell voltage of 1.501 V and higher stability in overall water electrolysis. This work provides a useful strategy to tune the electrocatalytic performance by doping engineering and hetero-interface formation that offers an efficient self-supported 3D heterostructure electrode material for overall water electrolysis.