We report on a complex study employing both theoretical and experimental methods with the aim of detailed elucidating the electronic and optical properties of potassium lead chloride, KPb2Cl5. In particular, we employ possibilities of X-ray photoelectron spectroscopy (XPS) to measure for an optical quality KPb2Cl5 crystal the binding energies of the core-level electrons as well as to elucidate the peculiarity of the energy distribution of the valence electrons associated with the atoms composing the compound under study. The XPS data reveal low hygroscopicity of the KPb2Cl5 crystal and minor transformation of the Pb2+ ions to Pb0 under treatment of the crystal surface with middle-energy Ar+ bombardment. Furthermore, in the present work we apply different approaches for exchange–correlation potential to find how different factors affect the theoretical curve of total density of states in comparison with the valence-band XPS spectrum. The Tran–Blaha modified Becke–Johnson (TB-mBJ) potential, including spin–orbital effect and the Coulomb repulsion (Hubbard parameter U), is found to give the most reliable theoretical electronic structure of KPb2Cl5. Based on these findings, detailed studies on the occupation of the valence and conduction bands by electronic states associated with the atoms composing the KPb2Cl5 compound as well as on the optical properties are performed in the present work.