An electrocatalyst with high performance can enhance the hydrogen production for overall water-splitting. This study reports on the e-waste-derived activated carbon encapsulated cobalt sulfide (CoS2/AC) nanocomposite synthesized via a simple hydrothermal process for overall water-splitting application. The microstructural image of CoS2/AC showed the aggregated stacked nanosheets of activated carbon encapsulating the cobalt sulfide nanoparticles. The nanocomposite of CoS2/AC exhibited the overpotential of 240 mV at 10 mA cm−2 and a 34 mV dec−1 of Tafel slope value with extraordinary stability for OER. On the other hand, the nanocomposite exhibited the overpotential of 378 mV at 10 mA cm−2 with a Tafel slope of ∼134 mV dec−1 with splendid stability in 1 M KOH solution for HER. The enhanced electrical conductivity and electrochemically active surface area of the AC nanosheets and CoS2 nanoparticles in this nanocomposite account for its higher electrocatalytic activity. Thus, the hydrothermally synthesized CoS2/AC presents itself as a better bifunctional catalyst for overall water-splitting.