We describe the process evaluation for a randomized controlled trial that compared group support psychotherapy (GSP) with group HIV education for treatment of depression among people with HIV. Process data were obtained using mixed methods. Variables evaluated were indicators of feasibility and acceptability; causal mediating processes and contextual influences. GSP was feasible and acceptable. Potential mediating variables between GSP and reduction of depression were improved emotional and social support, better coping strategies, and pursuit of livelihoods. Culturally sensitive intervention content facilitated intervention delivery. These data complement the trial outcomes, and may provide a contextualized description of how GSP treats depression.