Background Colorectal peritoneal metastases (CRPM) are associated with poor prognosis and limited systemic therapy options. While immune checkpoint inhibitors (ICI) have revolutionized treatment for mismatch repair–deficient (dMMR) and microsatellite instability–high (MSI‑H) metastatic colorectal cancer, outcomes in CRPM is unclear. The integration of ICIs with cytoreductive surgery (CRS) is unexplored, and optimal management strategies remain undefined. The aim of this review is to evaluate clinical effectiveness, survival, and surgical implications of ICI in CRPM. Methods We conducted a systematic review following PRISMA guidelines, searching PubMed, MEDLINE, Embase, and Google Scholar from inception to October 2025. Eligible studies included adults with CRPM treated with ICI, reporting clinical, radiological, pathological, or survival outcomes. Study quality was assessed using a modified Newcastle-Ottawa Scale, and findings were synthesised qualitatively Results Seventeen studies met inclusion criteria, comprising eight retrospective cohorts and nine case reports, totalling 564 patients. Only 6.2% of patients received ICI combined with CRS with or without HIPEC. Anti-PD-1-based regimens were most used, and all but one study involved dMMR/MSI-H disease. Partial or complete response rates ranged from 13-46%, and disease stability in 25-48%. Median overall survival of the entire cohort ranged from 7.4 to 35 months, with two-year survival rates of 64-75%, increasing to approximately 80% when ICI was combined with CRS. Conclusion Current evidence suggests that ICI can achieve partial or complete responses in selected patients with CRPM, particularly those with dMMR/MSI-H tumours. Survival may be further improved when combined with CRS. However, the evidence base is limited to retrospective data, highlighting the need for prospective trials to define optimal sequencing and patient selection.