The high reaction rate in the sol–gel combustion synthesis (SCS) often restricts precise control over the composition of mixed valent oxides in a single step. The current study overcomes this limitation by employing melamine—that forms a hydrogel with Cu(II)—as a novel fuel in the combustion synthesis. As opposed to the conventional SCS approach, the current synthesis occurs in a mild and controlled way under oxygen-lean conditions,wherein at and above 300 °C of calcination, a red-hot coke is found to form and persist for hours and hence termed as ‘soft sol–gel combustion synthesis’ (SSCS). Such a controlled synthesis is shown to be pivotal in obtaining a copper-based mixed-valent oxide/cermet nanocomposite system, comprising tunable levels of g-C3N4, in a single step. The phase compositions of the nanocomposites are modulated by varying calcination parameters like temperature and duration. These nanocomposites are thoroughly characterized for their microstructural, morphological, elemental, bandgap, and optical properties.Unique compositions are synthesized from the blend of Cu(II)–melamine complex gel with ZIF-8, in which formulations comprising different proportions of ZnO, CuO, Cu2O, metallic Cu and g-C3N4 have been obtained. Such multicomponent formulations post ball-milling exhibit notable photocatalytic activity in degrading organic pollutants and show high antibacterial efficacy against Escherichia coli under dark-light dual-mode conditions. Additionally, the SSCS approach has also been demonstrated for its versatility by synthesizing nickel-based cermet, which opens up numerous avenues for developing exotic material compositions for diverse applications in the realms of energy and environment.