BACKGROUND: Antiretroviral therapy (ART) substantially decreases morbidity and mortality in people living with HIV. In this study, we describe population-level trends in the adult life expectancy and trends in the residual burden of HIV mortality after the roll-out of a public sector ART programme in KwaZulu-Natal, South Africa, one of the populations with the most severe HIV epidemics in the world. METHODS: Data come from the Africa Centre Demographic Information System (ACDIS), an observational community cohort study in the uMkhanyakude district in northern KwaZulu-Natal, South Africa. We used non-parametric survival analysis methods to estimate gains in the population-wide life expectancy at age 15 years since the introduction of ART, and the shortfall of the population-wide adult life expectancy compared with that of the HIV-negative population (ie, the life expectancy deficit). Life expectancy gains and deficits were further disaggregated by age and cause of death with demographic decomposition methods. FINDINGS: Covering the calendar years 2001 through to 2014, we obtained information on 93???903 adults who jointly contribute 535???42 8 person-years of observation to the analyses and 9992 deaths. Since the roll-out of ART in 2004, adult life expectancy increased by 15??2 years for men (95% CI 12??4-17??8) and 17??2 years for women (14??5-20??2). Reductions in pulmonary tuberculosis and HIV-related mortality account for 79??7% of the total life expectancy gains in men (8??4 adult life-years), and 90??7% in women (12??8 adult life-years). For men, 9??5% is the result of a decline in external injuries. By 2014, the life expectancy deficit had decreased to 1??2 years for men (-2??9 to 5??8) and to 5??3 years for women (2??6-7??8). In 2011-14, pulmonary tuberculosis and HIV were responsible for 84??9% of the life expectancy deficit in men and 80??8% in women. INTERPRETATION: The burden of HIV on adult mortality in this population is rapidly shrinking, but remains large for women, despite their better engagement with HIV-care services. Gains in adult life-years lived as well as the present life expectancy deficit are almost exclusively due to differences in mortality attributed to HIV and pulmonary tuberculosis. FUNDING: Wellcome Trust, the Bill & Melinda Gates Foundation, and the National Institutes of Health.