Ferroelectric (K0.455Li0.045Na0.5)(Nb0.9Ta0.1)O3 + x mol% BaCO3 ceramic compositions with Ba2+ as an A-site dopant in the range of x = 0–1.2 mol% were synthesized by conventional ceramic processing route. Effect of Ba2+ content on the microstructure, ferroelectric, dielectric, and piezoelectric properties of the ceramics was investigated. The results of X-ray diffraction reveal that Ba2+ diffuse into the (K0.455Li0.045Na0.5)(Nb0.9Ta0.1)O3 lattices to form a solid solution with a perovskite structure having typical orthorhombic symmetry. As Ba2+ content increases, cell volume and tetragonality increase in the crystal structure of the ceramics. Increasing doping level of Ba2+ inhibits grain growth in the ceramics and reduces both the Curie temperature (Tc) and tetragonal–orthorhombic phase transition temperature (To-t). The bulk density, remnant polarization Pr, room-temperature dielectric constant (e′RT), planar electromechanical coupling factor kp, and piezoelectric charge coefficient d33 are found to increase as Ba2+ concentration increases from 0 to 0.8 mol% and then decrease as Ba2+ content increases further from 0.8 to 1.2 mol%. High piezoelectric properties of d33 = 187 pC/N and kp = 48 % are found in 0.8 mol% Ba2+ composition. Optimum amount of Ba2+ dopant takes the polymorphic phase boundary region consisting of orthorhombic and tetragonal crystal structures of the ceramic system near the room temperature and enhances its piezoelectric properties.