An effective methodology to deal with the theoretical treatment on the redox chemistry of divalent organolanthanide complexes is reported and has been tested on two representative substrates, pyridine and CO2, with two different metals (samarium and thulium). An influence of the ancillary ligands, namely, C5Me5 (Cp*) or (2,3,4,5-tetramethylphospholyl) (Tmp), on the one- or two-electron oxidation processes is observed. The theoretical results are in excellent agreement with the experimental observations indicating the efficiency of the method.