The electronic structure of a plutonium-based single-molecule magnet (SMM) was theoretically examined by means of multiconfigurational electronic structure theory calculations, including spin-orbit coupling effects. All Pu 5f to 5f transitions for all possible spin states were computed, as well as ligand to metal charge transfer and Pu 5f to 6d transitions. Spin-orbit coupling effects were included a posteriori to accurately describe the electronic transitions. The spin-orbit coupled energies and magnetic moments were then used to compute the magnetic susceptibility curves. The experimental electronic structure and magnetic susceptibility curve were reproduced well by our calculations. A compound with a modified electron-donating ligand (namely a carbene ligand) was also investigated in an attempt to tune the electronic properties of the plutonium SMM, revealing a higher ligand field splitting of the 5f orbitals of Pu, which could in turn enhance the barrier against magnetic relaxation.