Background: The rollout of antiretroviral therapy (ART) is one of the largest public health interventions in Eastern and Southern Africa of recent years. Its impact is well described in clinical cohort studies, but population-based evidence is rare. Methods: We use data from seven demographic surveillance sites that also conduct community-based HIV testing and collect information on the uptake of HIV services. We present crude death rates of adults (aged 15–64) for the period 2000–2011 by sex, HIV status, and treatment status. Parametric survival models are used to estimate age-adjusted trends in the mortality rates of people living with HIV (PLHIV) before and after the introduction of ART. Results: The pooled ALPHA Network dataset contains 2.4 million person-years of follow-up time, and 39114 deaths (6893 to PLHIV). The mortality rates of PLHIV have been relatively static before the availability of ART. Mortality declined rapidly thereafter, with typical declines between 10 and 20% per annum. Compared with the pre-ART era, the total decline in mortality rates of PLHIV exceeds 58% in all study sites with available data, and amounts to 84% for women in Masaka (Uganda). Mortality declines have been larger for women than for men; a result that is statistically significant in five sites. Apart from the early phase of treatment scale up, when the mortality of PLHIV on ART was often very high, mortality declines have been observed in PLHIV both on and off ART. Conclusion: The expansion of treatment has had a large and pervasive effect on adult mortality. Mortality declines have been more pronounced for women, a factor that is often attributed to women's greater engagement with HIV services. Improvements in the timing of ART initiation have contributed to mortality reductions in PLHIV on ART, but also among those who have not (yet) started treatment because they are increasingly selected for early stage disease.