A promising methanesulfonic acid (MSA) system, in lieu of conventional fluosilicic acid system, for green and efficient electro-refining of Pb, was proposed, due to its low volatility, low corrosivity, desired thermal stability and high conductivity. The electro-deposition behavior of the MSA-based Pb electro-refining (MPR) was explored, including its operation mechanism, reaction reversibility, nucleation, and growth mode. Based on cyclic voltammetry (CV) and chronoamperometry (CA), the diffusion-controlled and irreversible lead deposition process of MPR was revealed, and the theoretical model of MPR lead deposition nucleation and growth with transient nucleation was established. The bench-scale proof-of-concept operation of MPR achieved energy consumption of 104.22 kW·h/t Pb and current efficiency of 99.24%, which was competitive with the energy consumption of 120 kW·h/t Pb and current efficiency of 95% for H₂SiF₆ system. The bench-scale operation of MPR obtained a smooth and compact deposit sample with Pb purity of 99.9925%, which satisfied the standard of Pb ingot (GB/T 469—2013) of 99.97%.