Background: Successful completion and retention throughout the multi-step cascade of prevention of mother-to-child HIV transmission (PMTCT) remains difficult to achieve. The Mother and Infant Visit Adherence and Treatment Engagement study aims to evaluate the effect of mobile text messaging, community-based mentor mothers (cMMs), or both on increasing antiretroviral therapy (ART) adherence, retention in HIV care, maternal viral load suppression, and mother-to-child HIV transmission for mother-infant pairs receiving lifelong ART. Methods/design: This study is a cluster randomized, 2 × 2 factorial, controlled trial. The trial will be undertaken in the western Kenyan counties of Migori, Kisumu, and Homa Bay. Study sites will be randomized into one of four groups: six sites will implement both text messaging and cMM, six sites will implement cMM only, six sites will implement text messaging only, and six sites will implement the existing standard of care. The primary analysis will be based on the intention-to-treat principle and will compare maternal ART adherence and maternal retention in care. Discussion: This study will determine the impact of long-term (up to 12 months postpartum) text messaging and cMMs on retention in and adherence to ART among pregnant and breastfeeding women living with HIV in Kenya. It will address key gaps in our understanding of what interventions may successfully promote long-term retention in the PMTCT cascade of care.