Objective: This meta-analysis assessed the effectiveness of peer-administered interventions for treating perinatal depression or anxiety and whether variations in intervention characteristics impacted their effectiveness. Data Sources: Records were identified through MEDLINE, EMBASE, PsycINFO, CINAHL, and Web of Science until October 2024. We used terms related to the perinatal period, depression, anxiety, and peer support. Study Selection and Data Extraction: We identified 5,700 articles, of which 19 were included and 18 were meta-analyzed. A total of 3,821 participants were included, with the majority from high-income countries. Studies involving a peer-administered intervention for perinatal depression or anxiety with a randomized controlled trial (RCT) design were eligible. Three intervention types were identified: peer-delivered psychotherapies, individual peer support, and peer discussion groups. Results: Random-effects meta-analyses suggested that peer-administered interventions were more effective at improving depression symptoms than standard care (standardized mean difference [SMD]: -0.35; 95% CI, -0.54 to -0.17). Peer-delivered psychotherapy had the largest effect sizes (SMD: -0.51; 95% CI, -0.79 to -0.24), followed by individual support (SMD: -0.30; 95% CI, -0.63 to 0.04) and discussion groups (SMD: -0.09; 95% CI, -0.42 to 0.25). Subgroup analyses suggest that group interventions may lead to the greatest improvement. On the whole, peer-administered interventions were not effective for anxiety (SMD: -0.25; 95% CI, -0.57 to 0.08), but peer-delivered psychotherapies specifically improved anxiety symptoms (SMD: -0.63; 95% CI, -0.95 to -0.31). Conclusions: Peer-administered interventions are effective at improving perinatal depression, with peer-delivered psychotherapies being the most effective. Large-scale RCTs are needed to explore long-term effectiveness on perinatal depression and anxiety.