BACKGROUND: The impact of HIV stigma on viral suppression among people living with HIV (PLHIV) is not well characterized. SETTING: Twenty-one communities in Zambia and South Africa, nested within the HPTN 071 (PopART) trial. METHODS: We analyzed data on viral suppression (<400 copies HIV RNA/mL) among 5662 laboratory-confirmed PLHIV aged 18-44 years who were randomly sampled within the PopART trial population cohort 24 months after enrolment (PC24). We collected data on experiences and internalization of stigma from those PLHIV who self-reported their HIV status (n = 3963/5662) and data on perceptions of stigma from a 20% random sample of all PLHIV (n = 1154/5662). We also measured stigma at the community-level among PLHIV, community members, and health workers. We analyzed the association between individual- and community-level measures of HIV stigma and viral suppression among PLHIV, adjusting for confounding. RESULTS: Of all 5662 PLHIV, 69.1% were virally suppressed at PC24. Viral suppression was highest among those 3963 cohort participants who self-reported living with HIV and were on ART (88.3%), and lower among those not on treatment (37.5%). Self-identifying PLHIV who reported internalized stigma were less likely to be virally suppressed (75.0%) than those who did not (80.7%; adjusted risk ratio, 0.94 95% CI: 0.89 to 0.98). Experiences, perceptions, and community-level measures of stigma were not associated with viral suppression. CONCLUSION: Internalized stigma among PLHIV was associated with a lower level of viral suppression; other dimensions of stigma were not. Stigma reduction approaches that address internalized stigma should be an integral component of efforts to control the HIV epidemic.