Hexaniobate nanosheets (K_4−xH_xNb₆O₁₇) were combined with Cu²⁺ ions by grafting, a green one-step methodology. The resulted nanocomposite exhibits high surface area with most of the Cu²⁺ ions strongly connected to the hexaniobate layers as amorphous nanoclusters. Photocatalytic experiments evidence that the Cu-grafted hexaniobate can act as an efficient photocatalyst for H₂ evolution. The best performance for the Cu-grafted hexaniobate was reached when the Cu concentration was 0.5 wt% (1.62±0.10 mmo g⁻¹ h⁻¹), whereas hexaniobate layers with 0.5 wt % photodeposited Pt exhibited a hydrogen evolution rate of 0.95±0.04 mmol h⁻¹ g⁻¹ under the same experimental conditions. Grafting leads to covalently bounded Cu species onto the hexaniobate surface, ensuring a strong electronic interaction. Detailed XPS and EPR studies evidence that the initial Cu²⁺ species are promptly reduced to Cu¹⁺/Cu⁰ under illumination. The prominent performance of Cu-grafted samples was related to the improved charge-separation efficiency as shown by ns-transient spectroscopy. Therefore, the present methodology offers a green option to produce efficient Earth-abundant-based photocatalysts for H₂ evolution.