ZnS quantum dots are semiconductor nanoparticles characterized by superior optoelectronic properties. The amenability of these nanoparticles in initiating efficient photo-redox reactions enable their use as photocatalysts for environmental remediation. In the present study, ZnS quantum dots were biosynthesized from Zn tolerant Penicillium sp. under ambient reaction conditions. The biogenic ZnS quantum dots were characterized using TEM, SEM, XRD, FTIR and UV-Vis absorption studies that revealed the formation of spherical particles of average diameter 11.08 nm with a zinc blend crystal structure and the optical properties were in par with chemically synthesized ZnS. The biogenic ZnS were then used for the photodegradation of methylene blue (MB) dye. It was found that the green synthesized ZnS quantum dots exhibited good photocatalytic activity with a half-life of 4 h. Further, the dye degradation efficiency was enhanced as the ZnS nanocatalyst/dye ratio increased and reached equilibrium within 6 h. The present study reports an inexpensive and scalable method to fabricate ZnS nano hybrids with practical applicability in the remediation of pollutants in textile, paper and dyeing industry.