This study explores a water‐splitting activity using biphasic electrodeposited electrode on nickel foam (NF). The Ni9S8/Cu7S4/NF electrode with sulfur vacancy defects exhibits superior OER (oxygen evolution reaction) and HER (hydrogen evolution reaction) performance with reduced overpotential and a steeper Tafel slope. Ni9S8/Cu7S4/NF displays the ultra‐low overpotential value of 212 mV for OER and 109 mV for HER at the current density of 10 mA cm−2. The Tafel slope of 25.4 mV dec−1 for OER and 108 mV dec−1 for OER was found from that electrode. The maximum electrochemical surface area (ECSA), lowest series resistance and lowest charge transfer resistance are found in the sample with sulfur vacancy defects, showing increased electrical conductivity and quick charge transfer kinetics. Remarkably, the Ni9S8/Cu7S4/NF electrode demonstrated exceptional stability and was stable for 80 hours in pure water splitting and 20 hours in seawater splitting. The synergistic effect of using bimetallic (Cu & Ni) sulfide and enhanced electrical conductivity of the electrode are caused by sulfur vacancy defects resulting in improved water splitting performance.