Inclusion Criteria:
* Diagnosis of chronic migraine prior to the baseline phase based on the revised criteria for chronic migraine listed in International Classification of Headache Disorders (ICHD)-3 beta (2013)
* Fifteen or more headache days during the 4-week baseline phase, with each day consisting of 4 or more hours of continuous headache
* Routine non-headache medications of stable dose and regimen for at least 1 month prior to the start of screening.
Exclusion Criteria:
* Participants diagnosed with any of the following headache disorders: Familial hemiplegic migraine, Sporadic hemiplegic migraine, Migraine with brainstem aura, Migrainous infarction, Chronic tension-type headache, Hypnic headache, Hemicrania continua, New daily-persistent headache and Recurrent painful ophthalmoplegic neuropathy
* Participants with a confirmed history of medication overuse headache
* Participants with a diagnosis of retinal migraine, persistent aura without infarction or migraine-triggered seizure
* Headache attributable to another disorder (eg, cervical dystonia, craniotomy, head/neck trauma)
* Use of any headache prophylactic medication within 28 days prior to the start of the screening
* Any medical condition that may put the patient at increased risk with exposure to Botulinum Toxin Type A, including diagnosed myasthenia gravis, Eaton-Lambert syndrome, amyotrophic lateral sclerosis, or any other significant disease that might interfere with neuromuscular function
* Participants with a known or suspected Temporomandibular Disorder (TMD), including pain in or around the Temporomandibular Joint (TMJ)
* Participants with a concurrent diagnosis of fibromyalgia
* Previous treatment with botulinum toxin therapy for any reason, or immunization to any botulinum toxin serotype
* Acupuncture, transcutaneous electrical nerve stimulation (TENS), cranial traction, nociceptive trigeminal inhibition or occipital nerve block treatments, or injection of anesthetics or steroids into the study target muscles within 28 days prior to the start of the screening
* Unstable liver disease (as defined by the presence of ascites, encephalopathy, coagulopathy, hypoalbuminaemia, esophageal or gastric varices or persistent jaundice), cirrhosis, known biliary abnormalities (with the exception of Gilbert's syndrome or asymptomatic gallstones).
