The g-C3N4/TiO2 nanocomposites (NCs) are fabricated by optimization of calcination and subsequent hydrothermal technique decorated with CeO2 nanoparticles (NPs) to build the g-C3N4/TiO2–CeO2 hybrid NCs. The chemical and surface characterizations of structural, morphological, elemental composition, optical, photo-degradation, HER performance and the DFT computation has been efficiently analyzed. The g-C3N4/TiO2–CeO2 composite photocatalysts (PCs) exhibit photocatalytic improved performance (∼97 %) for MB aqueous dye related to pristine g-C3N4 and g-C3N4/TiO2 composite PCs. The obtained k value of the g-C3N4/TiO2/CeO2 heterostructure composite PCs has around 0.0262 min−1 and 6.1, 2.6 and 1.5 times higher than to g-C3N4 (0.0043 min−1), g-C3N4/CeO2 (0.0099 min−1) and g-C3N4/TiO2 (0.0180 min−1) PCs respectively. Likewise, the synergistic probable S-scheme charge separation mechanism based on scavengers’ tests and other values, which leads to effective separation of photo-excited (e−-h+) pairs, whereas high degradation and more H2O molecules have photo-reduction to H2. The H2 evolution reaction (HER) and the electrochemical impedance spectroscopy (EIS) of the as-obtained samples were explored via electrochemical study. This exertion recommends that the rational strategy and building of g-C3N4/TiO2–CeO2 nano-heterostructures were beneficial for developing visible-light-driven recyclable PCs for ecological refinement. Display omitted •CeO2 coupled g-C3N4/TiO2 photocatalyst was effectively prepared by a facile method.•Optimum degradation efficiency was 6.1 times higher than g-C3N4 under visible-light.•XPS and DFT study ensues a strong interface among Ti, Ce and O atoms into g-C3N4.•g-C3N4/TiO2/CeO2 S-scheme heterostructure exposed superior H2 production activity.•Also, good reusability for organic dye degradation and efficient HER performance.