Designing suitable heterojunctions effectively addresses challenges like rapid electron-hole recombination, limited mobility, restricted absorption, and insufficient active sites. Thus to improve the photocatalytic performance, we synthesized a p-n heterojunction photocatalyst, Co3O4/NiCo2O4@Mn0.2Cd0.8S, by coupling ZIF-67-derived p-type Co3O4/NiCo2O4 double-shelled nanocages with n-type Mn0.2Cd0.8S nanoneedles via a template-assisted method. Analytics revealed the judicious anchoring of the Mn0.2Cd0.8S over the Co3O4/NiCo2O4 surface, reinforcing the photocatalytic activity. The resultant heterostructure exhibits superior photocatalytic performance, achieving an HER rate of ∼14.34 mmol h−1 g−1 with an AQY of ∼35.1 %. This represents an enhancement of ∼72-fold compared to pristine Mn0.2Cd0.8S. The synergistic interplay within the heterostructure, facilitated by abundant active sites, enhanced light absorption, and an efficient charge transfer channel at the p-n heterojunction interface, promotes efficient photoexcited charge separation and transfer. Furthermore, the DFT calculations reveal that the incorporation of NiCo2O4 and Mn0.2Cd0.8S into the Co3O4 framework significantly reduces the HER overpotential from |ΔGH| = 0.32 eV for pristine Co3O4 to 0.20 eV for the Co3O4/NiCo2O4@Mn0.2Cd0.8S heterostructure. This enhancement is attributed to the optimized charge distribution at the active sites and a downward shift in the d-band centre from −2.15 eV to −2.30 eV, which weakens the adsorption of reaction intermediates, thereby accelerating HER kinetics.