L-edge core-level spectroscopy presents a significant challenge for electronic structure theory due to the simultaneous importance of electron correlation, orbital relaxation, and spin–orbit coupling effects. In this work, the density functional theory/multireference configuration interaction (DFT/MRCI) method is applied to the calculation of spin–orbit-coupled core-excited and core-ionized states relevant to L-edge X-ray absorption and X-ray photoelectron spectroscopy. The approach combines a density functional reference description with a multiconfigurational treatment of excited-state correlation, enabling computationally efficient treatment of electronically complex states while retaining important configuration interaction effects. Applications to heteroatom-containing molecular systems involving phosphorus, silicon, sulfur, and chlorine demonstrate that DFT/MRCI reproduces key spectral features, including spin–orbit splittings, state mixing, and relative transition intensities, at substantially lower computational cost than many conventional multireference approaches. These results highlight the potential of DFT/MRCI as a practical framework for the simulation of relativistic core-level spectroscopies in larger molecular systems.