This study, conducted in 7 African countries, aimed to assess the effect of antiretroviral therapy (ART) on HIV-1 transmission risk among heterosexual couples. The study followed 3381 serodiscordant couples for up to 24 months, with 349 HIV-1-infected partners initiating ART. The primary outcome was linked HIV-1 transmission, defined as seroconversion in the uninfected partner due to transmission from the infected partner. Only one transmission event occurred in the 349 ART-initiated couples, corresponding to a transmission rate of 0.37 per 100 person-years, compared to 2.24 per 100 person-years in those not on ART. ART initiation was associated with a 92% reduction in transmission risk, likely due to reduced plasma HIV-1 levels. The highest transmission risk was observed in couples where the infected partner had CD4 counts <200 cells/mm³ or plasma HIV-1 RNA concentrations >50,000 copies/mL. The study highlights the importance of ART in reducing HIV-1 transmission and emphasizes the need for maximizing ART coverage, especially in individuals with CD4 counts <200 cells/mm³.This study, conducted in 7 African countries, aimed to assess the effect of antiretroviral therapy (ART) on HIV-1 transmission risk among heterosexual couples. The study followed 3381 serodiscordant couples for up to 24 months, with 349 HIV-1-infected partners initiating ART. The primary outcome was linked HIV-1 transmission, defined as seroconversion in the uninfected partner due to transmission from the infected partner. Only one transmission event occurred in the 349 ART-initiated couples, corresponding to a transmission rate of 0.37 per 100 person-years, compared to 2.24 per 100 person-years in those not on ART. ART initiation was associated with a 92% reduction in transmission risk, likely due to reduced plasma HIV-1 levels. The highest transmission risk was observed in couples where the infected partner had CD4 counts <200 cells/mm³ or plasma HIV-1 RNA concentrations >50,000 copies/mL. The study highlights the importance of ART in reducing HIV-1 transmission and emphasizes the need for maximizing ART coverage, especially in individuals with CD4 counts <200 cells/mm³.