Objectives Population-based universal test and treat (UTT) trials have shown an impact on population-level virological suppression. We followed the ANRS 12249 TasP trial population for 6 years to determine whether the intervention had longer-term survival benefits. Methods The TasP trial was a cluster-randomized trial in South Africa from 2012 to 2016. All households were offered 6-monthly home-based HIV testing. Immediate antiretroviral therapy (ART) was offered through trial clinics to all people living with HIV (PLHIV) in intervention clusters and according to national guidelines in control clusters. After the trial, individuals attending the trial clinics were transferred to the public ART programme. Deaths were ascertained through annual demographic surveillance. Random-effects Poisson regression was used to estimate the effect of trial arm on mortality among (i) all PLHIV; (ii) PLHIV aware of their status and not on ART at trial entry; and (iii) PHLIV who started ART during the trial. Results Mortality rates among PLHIV were 9.3/1000 and 10.4/1000 person-years in the control and intervention arms, respectively. There was no evidence that the intervention decreased mortality among all PLHIV [adjusted rate ratio (aRR) = 1.10, 95% confidence interval (CI) = 0.85–1.43, p = 0.46] or among PLHIV who were aware of their status but not on ART. Among individuals who initiated ART, the intervention decreased mortality during the trial (aRR = 0.49, 95% CI = 0.28–0.85, p = 0.01), but not after the trial ended. Conclusions The ‘treat all’ strategy reduced mortality among individuals who started ART but not among all PLHIV. To achieve maximum benefit of immediate ART, barriers to ART uptake and retention in care need to be addressed.