Piezoelectric actuators are widely used industrial electronic devices. In recent years, driven by environmental concerns, lead-free piezoelectric materials, particularly KNN-based ceramics, have gained increasing attention. In this study, Mn-doped KNN piezoelectric ceramics were synthesized by the conventional solid-state reaction method and sintered in a reducing atmosphere. By employing a synergistic strategy involving defect dipoles and ferroelectric domain switching, a giant converse piezoelectric coefficient (d₃₃^*) of 2676 pm/V and a strain of 0.67% are achieved in the KNNM ceramics under an electric field of 2.5 kV/mm. In our ceramic samples, no obvious strain enhancement attributable to electrobending is observed. The ceramic exhibits excellent thermal stability, with performance degradation of less than 10% from room temperature to 170 ℃, and maintains favorable performance after 2 million fatigue cycles. Considering the combination of excellent piezoelectric properties, high temperature stability, superior fatigue resistance, and reduction resistance, KNNM ceramics are expected to facilitate the development of lead-free piezoelectric actuators compatible with base-metal internal electrodes.