Intrathyroid metastases are rare and often discovered incidentally. Hence, it is important to consider this differential when assessing thyroid masses, especially in patients with a history of non-thyroidal malignancy. A critical review of the literature was performed using data from both autopsy and clinical studies. Within clinical series, the most common source of secondary thyroid metastases are renal cell carcinomas followed by lung primaries. Metastases to the thyroid are more frequent in patients who have pre-existing thyroid pathology. There is no gender predominance with a median age between 54 to 68 years. Fine-needle aspiration, core-needle biopsy, and surgical resection with histological and immunohistochemical analysis are the main methods to confirm diagnosis. Molecular studies can identify mutations (such as EGFR, K-Ras, VHL) and translocations (such as EML4-ALK fusion) important in selecting candidates for target therapies. Patients with advanced-stage primary cancers, widespread dissemination, or unknown primary origin often have a poor prognosis. Systemic therapies, such as chemotherapy and hormonal therapy, are often used as adjuvant treatment post-operatively or in patients with disseminated disease. New targeted therapies, such as tyrosine kinase inhibitors and immune checkpoint inhibitors, have shown success in reported cases. Intrathyroid metastases require a high level of suspicion for diagnosis and tailored treatment based on primary tumour features, overall cancer burden and co-morbidities. This review provides a comprehensive update on the epidemiology, clinicopathological features and recent advancements in secondary thyroid cancer.