While stability, significantly poor apparent quantum efficiency (AQE < 0.5%) and over dependence on noble metal cocatalysts is a long standing problem, here, we report, for the first time, microwave-exfoliated p-type few-layer black phosphorous (BP-nanosheets) as a stable photocatalyst for hydrogen production without any supporting noble metal co-catalyst. This few layer BP has shown a record high apparent quantum efficiency (AQE) of ∼4% at 420 nm under visible light irradiation. This unprecedented AQE stems from a low level of material oxidation that impedes the degradation of BP under ambient conditions, strong absorption of photons at the surface, and a conduction band edge position that favorably facilitates the proton reduction reaction. These BP-nanosheets have also shown superior photocatalytic performance compared to the known cohort of metal-free photocatalysts such as graphitic carbon nitride, carbon dots, and red-P under identical experimental conditions. An understanding of the photo-physicochemical reasons that drive this chemistry is elucidated along with results obtained from physicochemical characterization and finite difference time domain simulations.