Multilayer ceramic actuator (MLCA) has been widely employed in actuators due to the large cumulative displacement under the low driving voltage. In this work, the MLCA devices consisting of a lead-free MnCO₃- and CuO-doped 0.96(K_0.48Na_0.52)(Nb_0.96Ta_0.04)O₃–0.04CaZrO₃ piezoelectric ceramics and a base nickel (Ni) metal inner electrode were well co-fired by the two-step sintering process in a reducing atmosphere. The ceramic layer/electrode interface is well-integrated and clearly continuous without distinct interdiffusion and chemical reaction, which is beneficial to the electrical reliability of the MLCA. As a result, the MLCA laminated with nine active ceramic layers obtains an ultrahigh piezoelectric coefficient d₃₃ of 3157 pC/N, about 9 times than bulk ceramics. The 0.5 mm-thick MLCA composed of a series of ~50 μm-thick ceramic layers and ~3 μm-thick Ni electrodes reaches a high 1.8 μm displacement under the low applied voltage of 200 V (the same displacement requires a voltage as high as 3700 V for ~1 mm-thick bulk ceramics). The excellent electrical performance and low-cost base electrode reveal that the (K,Na)NbO₃ (KNN)-based MLCAs are promising lead-free candidate for actuator application.