The activity and durability of electrocatalysts are important factors in their practical applications, such as electrocatalytic oxygen evolution reactions (OERs) used in water splitting cells and metal–air batteries. In this study, a novel electrocatalyst, comprising few-layered graphitic carbon (~5 atomic layers) encapsulated heazlewoodite (Ni₃S₂@C) nanoparticles (NPs), was designed and synthesized using a one-step solid phase pyrolysis method. In the OER test, the Ni₃S₂@C catalyst exhibited an overpotential of 298 mV at a current density of 10 mA·cm^–2, a Tafel slope of 51.3 mV·dec^–1, and charge transfer resistance of 22.0 Ω, which were better than those of benchmark RuO₂ and most nickel-sulfide-based catalysts previously reported. This improved performance was ascribed to the high electronic conductivity of the graphitic carbon encapsulating layers. Moreover, the encapsulation of graphitic carbon layers provided superb stability without noticeable oxidation or depletion of Ni₃S₂ NPs within the nanocomposite. Therefore, the strategy introduced in this work can benefit the development of highly stable metal sulfide electrocatalysts for energy conversion and storage applications, without sacrificing electrocatalytic activity.