Botulinum toxin type A (BT-A) is the first medication approved for the preventive treatment of chronic migraine (CM) and remains one of the few drugs available for this purpose. BT-A primarily acts on the nerve endings of the trigeminal and cervical nerves by inhibiting the release of inflammatory mediators such as calcitonin gene-related peptide, acetylcholine, and substance P. This reduces the binding of ionotropic and metabotropic receptors on neuronal membranes, thereby increasing the depolarization threshold of trigeminal and cervical nerve fibers and reducing their activation. However, certain aspects of its mechanism of action remain controversial. Clinically, the efficacy of BT-A in CM has been evaluated through large randomized placebo-controlled trials, such as the Phase 3 studies of the Phase Ⅲ Research Evaluating Migraine Prophylaxis Therapy (PREEMPT) trial. These findings have also been validated in multiple long-term observational studies. This review summarizes the evidence for using BT-A in the treatment of CM, outlines its mechanism of action, mode of action, and its safety and efficacy in preventive therapy, and discusses the current role of BT-A in pain management to provide a comprehensive understanding of the advancements in BT-A for chronic migraine treatment.