The luminescence properties of a single crystal of KYb(WO4)2 doped with Tb3+ are investigated as a function of temperature at ambient pressure and at room temperature under high hydrostatic pressure. The observed quenching of the green Tb3+ (5D4→7F5) luminescence is ascribed to a pressure-induced downshift of the Tb3+→W6+ metal to metal charge transfer (impurity trapped exciton) state. A model is introduced to account for the pressure-induced quenching of the Tb3+ luminescence at room temperature in this double tungstate crystal.