A ternary CuCoFe-LDH/g-C3N4/MoSe2 (LgM) composite was synthesized via simple co-precipitation method, demonstrating superior light-harvesting efficiency of 85 % over both UV and extended visible spectrum ranges. The observed shift in binding energy within the ternary system validated interfacial charge redistribution, resulting in the formation of a robust built-in electric field oriented from LDH/gCN to MS. Moreover, interface defects enhanced local electric fields, establishing active regions that facilitated charge separation and catalytic reactivity, thus elevating photocatalytic performance. Oxygen vacancies at the gCN/MS interface generated defect states extended the visible-light absorption and assisted charge-carrier dissociation, significantly improved the photocatalytic effectiveness of the ternary composite. Mott-Schottky study revealed that gCN and LDH function as n-type semiconductors with flat band potentials (Ef) of −0.86 V and −1.15 V, respectively, whilst MS displayed p-type features with an Ef of −0.64 V, signifying complementary electronic properties favourable for charge separation. The LgM composite displayed the best photocatalytic degradation for bisphenol A (BPA), under solar irradiation (67 %) and under LED illumination (53 %) within 6 h. Band structure modelling validated a Type-II charge transfer process primarily governed by superoxide radical-mediated catalytic degradation.