This systematic literature review and meta-analysis provide an overview of the critical role of gut microbiota in modulating the efficacy of immunotherapy for colorectal cancer. Gut microbes influence host immune responses through multiple mechanisms including modulation of immune cell activity, metabolite action, and immune tolerance. The ability of specific gut microbes to improve the efficacy of immune checkpoint inhibitors has been linked to their ability to improve gut barrier function, modulate immune cell activity, and produce key immunomodulatory metabolites such as short-chain fatty acids. In addition, the composition and diversity of the gut microbiota are strongly associated with the efficacy of immunotherapies, demonstrating the potential to improve therapeutic response by modifying the gut microbiota. This paper also discusses the prospect of manipulating the gut microbiota through strategies such as fecal microbial transplantation, probiotic supplementation, and dietary modifications to optimize the efficacy of immunotherapy.