The degradation of organic pollutants is significantly influenced by the recombination of photogenerated electron–hole pair, electron transfer and surface area of a photocatalyst. Barium titanate (BaTiO3) exhibits low photocatalytic activity due to the rapid recombination of photoinduced charge carriers. Hence, the photocatalytic performance of BaTiO3 (BTO) nanoparticles was improved by the construction of heterostructure with the addition of ZnS. BaTiO3 and ZnS were prepared using solid-state metathesis (SSM) and hydrothermal methods, respectively. Subsequently, a series of [(1-x)BaTiO3/(x)ZnS, x = 10, 30, 50 and 70 wt%] heterostructures were successfully constructed through a simple calcination method using pre-prepared BaTiO3 and ZnS. The XRD, FTIR, Raman, XPS and HRTEM analyses revealed the formation of heterostructure between the BTO and ZnS. The positron annihilation lifetime spectroscopy (PALS) results suggest the existence of defects within the materials. To explore the photocatalytic activity, the photodegradation of methyl orange (MO) dye was carried out under UV light illumination for 3 h. Among all the compositions, the heterostructure 70 BaTiO3/30 ZnS (BTZS(70-30)) demonstrated remarkable photocatalytic activity (91.38 %) which is 5.3 times higher than the pristine BTO (17.16 %). The improved photocatalytic activity of heterostructures may result from the effective charge carrier separation facilitated by the type –II band alignment structure between BTO and ZnS, as well as surface defects like oxygen (Vo), and sulphur (Vs) vacancies. The lowest photoluminescence of BTZS (70-30) clearly substantiated the observed high photocatalytic activity. The scavenger outcomes validated that superoxide radicals (•O2−) and holes (h+) played predominant role in the degradation of MO and a detailed explanation was provided for the plausible mechanism.