It is well-known that the performance of BiFeO₃BaTiO₃ (BF-BT) ceramics is sensitive to composition, calcining and sintering temperature (T_cal and T_sint) due to the formation of Bi₂₅FeO₃₉ and/or Bi₂Fe₄O₉ impurities and/or the volatilization of Bi₂O₃. We report remarkably stable electrical properties over the range of −0.03 ≤ x ≤ 0.05 and 930 ℃ ≤ T_sint ≤ 970 ℃ in 0.7Bi_(1+x)FeO₃-0.3BaTiO₃ ceramics prepared by one-step process. This method avoids the thermodynamically unstable region of BiFeO₃ and prevents the formation of Bi₂₅FeO₃₉ and/or Bi₂Fe₄O₉ impurities even when the addition of α-Bi₂O₃ raw material is intentionally deficient or rich to make off-stoichiometric BF-BT, thus greatly improving the robustness of compositional and processing. Rhombohedral-pseudocubic phase coexists in all ceramics, and their C_R/C_PC fraction are 48.0/52.0–50.6/49.4 and 55.9/44.1–56.6/43.4 when x increases from −0.05 ≤ x ≤ 0 to 0.01 ≤ x ≤ 0.05. The stable electrical properties of d₃₃ = 180–205 pC/N, P_r = 17.9–23.8 μC/cm², and T_C = 485–518 ℃ are achieved. The maximum d_33T/d_33RT of BF-BT is twice that of soft PZT, superior to most the-state-of-art lead-free ceramics. Our results provide a synthesis strategy for designing high performance piezoelectric materials with good stability and easy industrialization.