Eu²⁺–Mn²⁺ codoped orange-yellow-emitting Ba₃Lu(PO₄)₃ phosphors were synthesized by a solid-state reaction. The synthesis, structure refinement, and luminescence properties of the obtained phosphor were first investigated in detail. The crystal structure was refined with a split-atom model, where the oxygen atoms are distributed over two partially occupied sites. The refinement confirmed that BLuP:0.005Eu²⁺,0.06Mn²⁺ has a cubic unit cell with space group I3d (no. 220), cell parameters a = b = c = 10.4025 Å and Z = 4. The luminescent properties reveal that the developed phosphor can efficiently convert UV photons in a broad range from 230 to 430 nm into orange-yellow emission. On the basis of the luminescence spectra and fluorescence decay curves, we confirm that the energy transfer process from the Eu²⁺ to Mn²⁺ ions takes place in the codoped Ba₃Lu(PO₄)₃:Eu²⁺,Mn²⁺ phosphor, and the energy transfer efficiency increases with an increase in the Mn²⁺ content. The possible energy transfer mechanism was proposed in terms of the experimental results and analysis. In particular, our developed phosphor contains a larger amount of the red-emitting component, compared with the commercial YAG:Ce phosphor, possessing favorable properties for application in warm white LEDs with low correlated color temperature.