Bistable electrical switching of high-efficiency grating diffractions is realized by adding a front π-bistable twisted nematic (π-BTN) cell to a passive liquid crystal polarization grating (LCPG). The π-BTN cell can be switched between stable non- and 180°-twisted states, acting as a polarization converter that switches the polarization of a laser beam and thus changes the diffraction behavior of the LCPG. Both states of the π-BTN cell are stable and can be reversibly switched to each other by applying a voltage pulse of different frequencies. We experimentally demonstrate two bistable-switching operations: (i) the BTN-LCPG can either split or deflect the laser beam; and (ii) the BTN-LCPG can selectively diffract the laser beam to the +1st and -1st orders, while maintaining a high diffraction efficiency of ∼90%. With electrical switchability, a simple optical design, and low power consumption, the proposed BTN-LCPG concept is favorable in various applications.