Background: The universal test-and-treat strategy (UTT) aims to maximize population viral suppression (PVS), i.e. the proportion of all people living with HIV (PLHIV) on antiretroviral treatment (ART) and virally suppressed in a community. We investigated whether PVS improved during the course of the ANRS 12249 TasP trial conducted in rural South Africa and investigating UTT impact on HIV incidence. Methods: The TasP cluster-randomized trial (2012-2016) implemented six-monthly repeat home-based HIV counselling and testing (RHBCT) and referral of PLHIV to local HIV clinics in 2×11 clusters opened sequentially. ART was initiated according to national guidelines in control clusters and regardless of CD 4 count in intervention clusters. We measured residency status, HIV status and HIV care status for each participant. PVS was computed per cluster among all resident PLHIV (≥16, including those not in care) at cluster opening and daily thereafter. We used a mixed linear model to explore time patterns in PVS, adjusting for sociodemographic changes at cluster level. Findings: 8 563 PLHIV were followed. Between cluster opening and January 1, 2016, PVS increased significantly in both arms (intervention: 23·5% to 46·2%, +22·8, p<0·001; control: 26·0% to 44·6%, +18·6, p < 0·001), but not differently by arm (p=0·514). In the final adjusted model, PVS increase was most associated with increased RHBCT (measured by time since cluster opening). Contextual changes (measured by calendar time) also contributed slightly. The effect of universal ART was positive but not significant. Conclusions: Changes in ART initiation guidelines alone are not enough to significantly increase PVS. Trial Registration Number: The trial was also registered on ClinicalTrials.gov: NCT01509508 and South African National Clinical Trials Register: DOH-27-0512-3974. Funding Statement: This trial was sponsored by the French National Agency for AIDS and Viral Hepatitis Research (ANRS; grant number, 2011-375), and funded by the AN S, the Deutsche esellschaft f r Internationale Zusammenarbeit (GIZ; grant number, 81151938), and the International Initiative for Impact Evaluation, Inc. (3ie) with support from the Bill & Melinda Gates Foundation. The content is solely the responsibility of the authors and does not represent the official views of 3ie or the Bill & Melinda Gates Foundation. This trial was done with the support of Merck and Gilead Sciences, which provided the Atripla drug supply. The Africa Health Research Institute, (previously Africa Centre for Population Health, University of KwaZulu-Natal, South Africa) receives core funding from the Wellcome Trust, which provides the platform for the population-based and clinic-based research at the centre. Declaration of Interests: CI received honoraria for consulting services rendered to Gilead Sciences. All other authors declare that they have no conflicts of interest. Ethics Approval Statement: The Biomedical Research Ethics Committee (BREC), University of KwaZulu-Natal, South Africa (BFC 104/11) and the Medicines Control Council of South Africa approved the trial.