In this paper, we proposed an effective strategy to overcome the trade-off between piezoelectric coefficient and the Curie temperature via co-doping of K⁺ and Nb⁵⁺ ions at A/B sites, achieving a combination of high T_C and d₃₃ in BiFeO₃-BaTiO₃-based ceramics. The MPB region was confirmed in a very narrow range of x = 0.0075–0.01 by the Rietveld refinement of XRD patterns and Raman spectroscopy deconvolution. An optimized composition with 1 mol% K/Nb co-dopants possesses a high Curie temperature (T_C = 604 °C) along with d₃₃ = 163 pC/N, k_p = 43 %, P_r = 57.94 μC/cm²， and P_s = 68.18 μC/cm². An outstanding thermal stability to 540 °C was verified via the temperature dependence of d₃₃ and in situ Raman spectroscopy. This work not only affords a potential lead-free candidate material for the high-temperature piezoelectric application, but also provides a feasible strategy to design high-temperature dielectrics by exploiting the site engineering.