Early antiretroviral therapy (ART) initiation is a recommended public health approach for the prevention of HIV-1 transmission. In this cohort study, we included 13132 serodiscordant couples. ART was initiated for patients with CD4+ T cell counts less than 200 cells/uL, 350 cells/uL, and 500 cells/uL respectively. This divided the ART treated couples into three groups. Univariate and multivariate intention-to-treat analyses were performed to examine the association between the study groups. Early-ART initiation was associated with a 45% lower risk of partner infection than was late-ART initiation (AHR 0.55, 95% CI, 0.37-0.81). Mid-ART initiation was associated with a 39% lower risk of partner infection than was late-ART initiation (AHR 0.61, 95% CI, 0.48-0.78). However, the risk reduction between the early and mid-ART groups was not significant. Drug compliance (AHR 1.55, 95% CI 1.03-2.35) and increased baseline viral load (AHR 1.41, 95% CI 1.33-1.51) were associated with an increased risk of infections among partners in the treatment. Prevention of HIV transmission as a result of early ART initiation was feasible on national and regional scales; however, many factors, such as the motivation to commence ART, adherence, and attrition, may affect the impact of this strategy in programmatic settings.