Introduction: People living with HIV (PLWH) need to adhere to antiretroviral therapy (ART) to achieve optimal health. One reason for ART nonadherence is HIV-related stigma. Objectives: We aimed to examine whether HIV treatment self-efficacy (an intrapersonal mechanism) mediates the stigma-adherence association. We also examined whether self-efficacy and the concern about being seen while taking HIV medication (an interpersonal mechanism) are parallel mediators independent of each other. Methods: A total of 180 people living with HIV self-reported internalized HIV stigma, ART adherence, HIV treatment self-efficacy, and concerns about being seen while taking HIV medication. We calculated bias-corrected 95% confidence intervals for indirect effects using bootstrapping to conduct mediation analyses. Results: Adherence self-efficacy mediated the relationship between internalized stigma and ART adherence. Additionally, self-efficacy and concern about being seen while taking HIV medication uniquely mediated and explained almost all the stigma-adherence association in independent paths (parallel mediation). Conclusion: These results can inform intervention strategies to promote ART adherence.