Genetically encoded voltage indicators (GEVIs) enable noninvasive, highspeed monitoring of electrical activity but are constrained by limited brightness and rapid photobleaching under continuous illumination. Here, we present Vega, a highly photostable green fluorescence GEVI with both high sensitivity ({Delta}F/F{square}={square}-33% per 100{square}mV) and fast response (1.34{square}ms). Under onephoton excitation at 1 W/cm2, Vega exhibits more than 20-fold slower photobleaching than the spectrally similar GEVI, Ace-mNeon2. In acute mouse brain slice, Vega enabled widefield high-fidelity recording of action potentials from 51 neurons simultaneously. In pancreatic islets, it revealed heterogeneous {beta}-cell activation and intercellular coupling in response to glucose elevation. Finally, onephoton imaging in awake mice demonstrated stable cortical voltage mapping in vivo. Vega thus overcomes the longstanding photostability-performance tradeoff, enabling chronic, highfidelity voltage imaging across preparations.