A Study to Evaluate the Efficacy and Safety of Remibrutinib in Secondary Progressive Multiple Sclerosis

Inclusion Criteria: * Signed informed consent must be obtained prior to any assessment performed. * Male or female participants aged 18-65 (inclusive) at Screening. * Diagnosis of MS according to the 2017 revised McDonald criteria (Thompson et al 2018), with current SPMS in accordance with the revised clinical course (Lublin et al 2014) at Screening * Absence of documented clinical relapses in the 24 months before Screening and randomization. * EDSS score of 3.0 to 6.0 (inclusive) at Screening. * Documented evidence of disability progression in the 12 months before Screening. Exclusion Criteria: * Unwilling or unable to undergo MRI scans as per protocol (for example, claustrophobia, or presents absolute contraindications to MRI (e.g., metallic implants, metallic foreign bodies, pacemaker, defibrillator)). * History of clinically significant central nervous system (CNS) disease (e.g. stroke, traumatic brain or spinal injury, history or presence of myelopathy) or neurological disorders which may mimic multiple sclerosis (MS). * Ongoing substance abuse (drug or alcohol) or any other factor (e.g. serious psychiatric condition) that may interfere with the participant's ability to cooperate and comply with the study procedures. * Participants with history of confirmed Progressive Multifocal Leukoencephalopathy (PML) or neurological symptoms consistent with PML. * Women of childbearing potential (WOCBP), unless they are using highly effective methods of contraception (failure rate \< 1% per year) while taking study treatment and for at least 1 week after stopping study treatment. * Significant bleeding risk or coagulation disorders, at Screening. * Use of exclusionary medication prior to Screening/randomization as listed in the protocol. Other protocol-defined inclusion/exclusion critria may apply