Maternal HIV-1–specific antibodies are efficiently transferred to newborns, but their role in disease control is unknown. We administered neutralizing IgG, including the human neutralizing monoclonal IgG1b12, at levels insufficient to block infection, to six newborn macaques before oral challenge with simian-HIV strain SF162P3 (SHIV_SF162P3). All of the macaques rapidly developed neutralizing antibodies and had significantly reduced plasma viremia for six months. These studies support the use of neutralizing antibodies in enhancing B cell responses and viral control in perinatal settings.