Antiretroviral therapy (ART) could curtail the HIV epidemic, but its impact is diminished by low uptake. We developed a peer navigation program to enhance engagement in HIV care, ART adherence, and behavioral prevention. In preparation for a randomized controlled trial, the program was piloted over four months at two primary health clinics in South Africa's North West Province. Newly diagnosed, HIV-positive clients met regularly with navigators to address barriers to care, adherence, and prevention. To assess program acceptability and feasibility and characterize the mechanisms of action, we surveyed 25 clients who completed navigation services and conducted interviews with 10 clients, four navigators, and five clinic providers. Clients expressed near universal approval for the program and were satisfied with the frequency of contact with navigators. HIV stigma emerged as a primary driver of barriers to care. Navigators helped clients overcome feelings of shame through education and by modeling how to live successfully with HIV. They addressed discrimination fears by helping clients disclose to trusted individuals. These actions, in turn, facilitated clients' care engagement, ART adherence, and HIV prevention efforts. The findings suggest peer navigation is a feasible approach with potential to maximize the impact of ART-based HIV treatment and prevention strategies.