African swine fever virus (ASFV) causes a highly lethal swine disease that is currently present in many countries of Eastern Europe, the Russian Federation, and Southeast Asia, severely affecting the pig industry. Despite extensive research, effective vaccines or antiviral strategies are still lacking and relevant gaps in knowledge of the fundamental biology of the viral infection cycle exist. In this study, we identified pE199L, a protein of the inner viral membrane that is required for virus entry. More specifically, pE199L is necessary for the fusion event that leads to the penetration of the genome-containing core in the host cell. Our results significantly increase our knowledge of the process of internalization of African swine fever virus, which may instruct future research on antiviral strategies.