Cu- and V-doped BNKT10-based piezoelectric ceramics with up to 0.5 at.% dopant concentration were synthesized and displayed more homogeneous grain growth compared to undoped BNKT10 ceramics. The defect chemistry and defect structure, studied by X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR), indicate a slightly rhombic electronic environment with major unidirectional octahedral distortion of the local environment of Cu. The solubility limit of Cu2+ in this material system is lower than 0.05 at.% Cu; above this limit, a Cu segregation at the grain boundaries is prevalent, unlike in PZT and KNN. Here, V was shown to be incorporated into the perovskite lattice and possess oxidation states of +4 and +5, acting both as isovalent and donor dopant, predominantly compensated by A-site vacancies. A trend toward higher ceramic densities, higher maximum polarization, and higher remanent polarization with increasing Cu concentration was observed. A maximum mechanical coupling factor could be obtained in the case of doping with 0.4 at.% V and 0.1 at.% Cu with a planar coupling of 0.19 and a thickness coupling factor of 0.56.