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Double perovskites represent a class of materials with promising fundamental properties and a broad spectrum of potential applications. However, the wide bandgap energy in double perovskites presents a hindrance to further enhancement of their photovoltaic efficiency. In the present study, a high-pressure technique is employed to tune the bandgap energy of double perovskite Co₃TeO₆ (CTO). A giant bandgap reduction of ∼37% from 2.93 to 1.85 eV has been observed after high-pressure treatment. Subsequent synchrotron-based X-ray diffraction and Raman spectroscopy results reveal that the significant bandgap reduction of CTO accompanies a sequence of structural phase transitions during compression and decompression. Furthermore, the high-pressure phase with a smaller bandgap energy of 1.85 eV turns out to be quenchable to ambient conditions, making the quenched CTO a promising light-harvesting material for photovoltaic applications. The present results demonstrate that high pressure can represent a green and efficient technique to tune the properties of multifunctional materials and serve as a guide for searching for stable and environmentally friendly light-harvesting materials.