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Thyroid carcinoma (TC) is the most common cancer of the endocrine system worldwide, and its incidence has remained stable over the past forty years. Complex hormonal and environmental factors influence TC progression. The gut microbiome, a pivotal mediator in maintaining host physiology and the development of pathology, serves as a biomarker and therapeutic target in cancer immunotherapy. The microbiome-assisted tumor microenvironment (TME) sustains tumors through the modulation of multiple mechanisms. Immune suppression in the TME induces a metastatic phenotype of tumor cells by modulating signaling pathways, cell differentiation, and the innate immune response. Current research has confirmed that gut dysbiosis, bacterial outer membrane components (such as lipopolysaccharides and LPS), and metabolites (such as short-chain fatty acids and SCFAs) have bidirectional regulatory effects on thyroid function. However, the role of the local microbiome in modulating treatment responses and its interactions with the immune TME of TC remains unknown. The literature was searched in PubMed, Web of Science, and Google Scholar using keywords associated with "microbiome" and "thyroid carcinoma". Research articles, clinical trials, letters, and meta-analyses were published by January 2026. This narrative review summarizes the role of the intratumor microbiome in tumor progression, interactions with chemotherapy, radiotherapy, and targeted therapies. The associations between the microbiome and the immune TME of cancers, as well as the characteristics of the immune TME and alterations in the gut/intratumor microbiome in patients with TC receiving different therapies, are discussed. Mediating microbiome and metabolites might be potential strategies for optimizing personalized therapeutic interventions against TC. Future research should focus on defining microbial signatures associated with treatment success and developing targeted strategies to improve patient outcomes on the basis of microbiome modulation.