Herein, we report the performance of a photocatalytic system based on visible-light active MIL-125-NH 2 mixed with nickel phosphide (Ni 2 P) nanoparticles. This combination boosts the H 2 evolution rate to an outstanding value of 894 μmol h −1 g −1 under visible-light irradiation, which is among the highest H 2 evolution rates reported to date for metal-organic frameworks (MOFs). The H 2 generation rate exhibited by Ni 2 P/MIL-125-NH 2 is almost 3 times higher than that of the Pt/MIL-125-NH 2 system, highlighting the impact of the co-catalyst on photocatalytic water splitting. Additionally, our system outperforms the Ni 2 P/TiO 2 system under UV-vis irradiation. The exceptional performance of Ni 2 P/MIL-125-NH 2 is due to the efficient transfer of photogenerated electrons from MIL-125-NH 2 to Ni 2 P, high intrinsic activity of Ni 2 P and exceptional synergy between them. This system exhibits the highest apparent quantum yields of 27.0 and 6.6% at 400 and 450 nm, respectively, ever reported for MOFs. We showcase the key role of the co-catalyst when combined with MIL-125-NH 2 towards the photocatalytic H 2 generation.