We report herein a first-principles investigation on electronic properties and 4f→5d transitions of Ce³⁺ substituted at La³⁺ and Ca²⁺ sites of La₂CaB₁₀O₁₉ (LCB) crystal, using the hybrid density functional theory (DFT) and the wave function-based embedded cluster calculations, respectively. The hybrid DFT with PBE0 functional yields a band gap of 8.1 eV for LCB, in good agreement with the experimentally estimated value of ∼8.3 eV. The energy gaps between the occupied Ce³⁺ 4f states and the valence band maximum of the host are predicted to be 1.93 ± 0.12 eV, with a slight dependence on the local environment. Based on the results of embedded cluster calculations at the CASSCF/CASPT2 level with the spin–orbit effect, the experimentally observed excitation bands are identified in association with the two cerium substitutions. The difference between the lowest 4f→5d transition energies of Ce³⁺ located at the two dopant sites are rationalized in terms of the variations in centroid energy and crystal-field splitting of the 5d¹ configuration with the local environment.