The effect of electric poling on the piezoelectric properties of the sintered Na_0.4K_0.1Bi_0.5TiO₃ is studied with varying poling field and temperature. An optimized poling condition (E_P =50 kVcm, T_P =110 °C) exhibited a high piezoelectric voltage (g₃₃∼ 85 mV m/N) and charge coefficients (d₃₃∼193pC/N). A combination of electric field induced irreversible transformation from polar nano regions embedded in a non-polar relaxor state to a long-range ordered ferroelectric state and increase in the structural ordering are responsible for the observed high piezoelectric properties. A mechanism is discussed to reveal the origin of high voltage coefficient due to poling, where the decrease of dielectric permittivity can facilitate high g₃₃. This investigation provides an approach for designing the high performance Na_0.4K_0.1Bi_0.5TiO₃based materials suitable for sensors and energy harvesting applications.