Scalable solutions to treat depression in older adults in low-resourced settings are urgently needed. The PRODIGITAL-D pragmatic, single-blind, two-arm, individually randomized controlled trial assessed the effectiveness of a mobile messaging psychosocial intervention in improving depressive symptomatology among older adults in socioeconomically deprived areas of Guarulhos, Brazil. Older adults (aged 60+ years) registered with 24 primary care clinics and identified with depressive symptomatology (9-item Patient Health Questionnaire (PHQ-9) scores ≥ 10) received the 6-week Viva Vida intervention based on psychoeducation and behavioral activation (n = 298) or a single message (n = 305). No health professional support was offered. The primary outcome was improvement from depressive symptomatology (PHQ-9 < 10) at 3 months. Of the 603 participants enrolled (mean age = 65.1 years; 451 (74.8%) women), 527 (87.4%) completed the follow-up assessment. In the intervention arm, 109 of 257 (42.4%) participants had an improved depressive symptomatology, compared with 87 of 270 (32.2%) participants in the control arm (adjusted odds ratio = 1.57; 95% confidence interval = 1.07-2.29; P = 0.019). No severe adverse events related to trial participation were observed. These results demonstrate the usefulness of a digital messaging psychosocial intervention in the short-term improvement from depressive symptomatology that can potentially be integrated into primary care programs for treating older adults with depression. Brazilian Registry of Clinical Trials registration: ReBEC ( RBR-4c94dtn ).