Common mental disorders (CMDs) such as depression and anxiety are highly prevalent among older adults. While psychosocial interventions are increasingly recognized for their preventive potential, a comprehensive synthesis of their effectiveness with nonclinical elderly populations is pending. This study aimed to evaluate the effectiveness of such interventions in reducing depressive and anxiety symptoms among older adults with subclinical symptom levels and to examine potential moderators (that is, intervention type, length, delivery modality, and control group characteristics). A meta-analysis was conducted of 58 randomized controlled trials (RCTs) testing psychosocial interventions aimed at preventing depression and/or anxiety, using validated measures and targeting adults aged ≥60. Moderator variable effects were assessed through mixed-effects meta-regressions, and effect generality was examined using multiverse analyses. Psychosocial interventions showed a moderate postintervention effect in reducing depressive symptoms (d = −0.474) that remained nontrivial and modest at follow-up (d = −0.386) compared to control. For anxiety, a small-to-moderate effect was observed postintervention (d = −0.333), with a small, albeit nominally nonsignificant, effect at follow-up (d = −0.205) compared to control. No significant differences were found between intervention types or control conditions. Younger participants experienced greater reductions in depressive symptoms from pre-to-post-intervention and at follow-up, and in anxiety symptoms from pre-to-post-intervention only. Multiverse analyses showed that intervention effects generalized across numerous variables, thus indicating a remarkable robustness of the findings. Our findings demonstrate that it is important to implement psychosocial interventions in community settings, regardless of intervention type, to protect the elderly against CMDs.