The synthesis of high-entropy metal chalcogenides has long been constrained by the constraints of high-temperature synthesis, a process that is both time-intensive and energy-demanding due to formidable entropic barriers. Herein, we report a rapid, cost-effective, and ambient-temperature synthesis of high-entropy metal chalcogenides entirely in aqueous solution. This mild yet potent approach facilitates the formation of (NiCoFeMnCr)S, (NiCoFeMnCr)Se and (NiCoFeMnCr)Te which exhibit outstanding performance for the oxygen evolution reaction, urea oxidation and wastewater treatment. Remarkably, this method is readily scalable, capable of producing over 100 grams of high-entropy sulfide materials in a single batch. This work establishes a versatile and sustainable pathway for the low-temperature, large-scale synthesis of diverse high-entropy nanomaterials, broadening the synthetic landscape for next-generation energy and environmental technologies.