In this study, a novel, simple and sensitive square wave voltammetric method for the determination of elbasvir (ELB) using the Mn5O8-modified pencil graphite electrode (PGE) was developed. Mn5O8 nanoparticles (NPs) were synthesized by calcination of manganese malonate at 350 °C for 24 h. The structure of Mn5O8 was characterized by X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) and Raman spectroscopy. Nitrogen adsorption-desorption measurements have shown that Mn5O8 NPs possess a mesoporous structure with a specific surface area of ~32 m2/g. After characterization, Mn5O8 NPs were applied to the electrode surface in a "drop-casting" fashion. Scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and square wave voltammetry (SWV) were employed to investigate the differences between the Mn5O8-decorated PGE and bare PGE. Under the optimized experimental conditions, the modified PGE gives a linear response over the concentration range of 0.20 to 3.00 μmol L-1 ELB with low limits of detection and quantitation, which were found to be 0.04 and 0.13 μmol L-1, respectively. For the first time, the photo-stability and the photo-induced dimeric-monomeric conversion behavior of ELB were studied using FT-IR, spectrophotometric, spectrofluorimetric and mass spectroscopic techniques. The fabricated electrode exhibits good precision, selectivity, and sensitivity that could be applied successfully for sensitive determination of ELB in its bulk form, in quality control laboratories and biological fluids.