Owing to the global energy crisis and serious environmental contamination, there is an urgent need to search for highly active and stable non-noble metal based electrocatalysts to reduce the energy losses for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) but it is still a significant challenge. In this work, self-supported Mo-doped Ni₃S₂ (denoted as Mo-Ni₃S₂/NF) was successfully assembled via a facile one-step hydrothermal method and used as a bifunctional electrocatalyst. A series of controllable morphologies were achieved by changing the molar ratios of reactants to study the influencing factors of electrocatalytic activity. The as-obtained Mo-doped Ni₃S₂/NF nanoneedles exhibit excellent electrocatalytic activities with a low overpotential of 170 mV to deliver a current density of 10 mA cm⁻² for the HER and an excellent overpotential of 174 mV at a current density of 50 mA cm⁻² for the OER. When used as both a cathode and an anode for overall water splitting in two electrode configuration (1 M KOH aqueous electrolyte), Mo-Ni₃S₂/NF nanoneedles exhibit outstanding activity (an external voltage of 1.49 V to display a stable current density of 10 mA cm⁻²) and impressive durability (no obvious degradation at a constant voltage for up to 24 h). This work provides a promising avenue of incorporating the nanostructure design with compositional modulation to synthesize bifunctional electrocatalysts of superior activity and delicate stability.