We investigated the effect of early antiretroviral treatment (ART) initiation on HIV status disclosure and social support in a cluster-randomized, treatment-as-prevention (TasP) trial in rural South Africa. Individuals identified HIV-positive after home-based testing were referred to trial clinics where they were invited to initiate ART immediately irrespective of CD4 count (intervention arm) or following national guidelines (control arm). We used Poisson mixed effects models to assess the independent effects of (a) time since baseline clinical visit, (b) trial arm, and (c) ART initiation on HIV disclosure (n = 182) and social support (n = 152) among participants with a CD4 count > 500 cells/mm(3) at baseline. Disclosure and social support significantly improved over follow-up in both arms. Disclosure was higher (incidence rate ratio [95% confidence interval]: 1.24 [1.04; 1.48]), and social support increased faster (1.22 [1.02; 1.46]) in the intervention arm than in the control arm. ART initiation improved both disclosure and social support (1.50 [1.28; 1.75] and 1.34 [1.12; 1.61], respectively), a stronger effect being seen in the intervention arm for social support (1.50 [1.12; 2.01]). Besides clinical benefits, early ART initiation may also improve psychosocial outcomes. This should further encourage countries to implement universal test-and-treat strategies.