Several mechanisms for the electropolymerization of pyrrole have been proposed since the first report 40 years ago. However, none of them were consensual despite a range of assumptions. We simulated and explained the preliminary steps governing the electropolymerization of pyrrole in a charged model interface using first-principles molecular dynamics calculations to solve the problem. We have shown under these conditions that adjacent pyrrole molecules in water can react together, causing their electropolymerization at the interface with a biased platinum electrode in anodic oxidation. In this work, the effective screening medium method that prevents energy divergence of the system was applied to different configurations of pyrrole, water, and electrolyte molecules to best screen the phase space. Furthermore, we worked on a Pt(100) electrode surface in an aqueous electrolyte to be as close as possible to the experimental conditions, MD taking the average of their different orientations.