Detection of residual organic and inorganic species in water bodies including drinking water has led to developing strategies for their removal. Here we report a very efficient method of photoreduction of Cr (VI) and photodegradation of methylene blue dye in aqueous medium using Z-scheme heterojunction based Sn3O4/SnS2 solar photocatalyst. The photocatalyst is synthesized by hydrothermal route and it is thoroughly characterized in terms of its structural, compositional, morphological and optical properties. About 100 % of Cr (VI) reduction in 60 min and 99.6 % of methylene blue degradation in 90 min is achieve under sunlight exposure at a photocatalytic rate of 0.066 min-1 and 0.043 min-1, respectively. The total organic carbon estimation of the post-degradation reaction medium corresponded to 85.1 % (MB) mineralization. The photocatalytic degradation is attributed to in-situ generation of reactive oxygen species (ROS) e.g., superoxide radicals, hydroxide radicals, and the role of ROS towards reduction and degradation of Cr (VI) and MB respectively, is confirmed from ROS scavenging studies. The dye degradation mechanism has been discussed by analyzing the degradation products via UPLC-Q-Tof-MS. The photocatalytic degradation of methylene blue by Sn3O4/SnS2 nanocomposites is significantly enhanced as compared to SnS2 photocatalyst, attributed to Z-scheme heterojunction and the charge carrier mobility.