A Study to Investigate the Efficacy of Fenebrutinib in Relapsing Multiple Sclerosis (RMS)

Inclusion Criteria: * A diagnosis of RMS in accordance with the revised 2017 McDonald Criteria. * Expanded Disability Status Scale (EDSS) score of 0 - 5.5 at screening. * For female participants of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraceptive measures, and refrain from donating eggs. * For male participants: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraceptive measures, and refrain from donating sperm. Exclusion Criteria: * Disease duration of \> 10 years from the onset of symptoms and an EDSS score at screening \< 2.0. * Female participants who are pregnant or breastfeeding, or intending to become pregnant. * Male participants who intend to father a child during the study. * A diagnosis of Primary Progressive Multiple Sclerosis (PPMS) or non-active Secondary Progressive Multiple Sclerosis (SPMS). * Any known or suspected active infection at screening, including but not limited to a positive screening tests for Hepatitis B and C, an active or latent or inadequately treated infection with tuberculosis (TB), a confirmed or suspected progressive multifocal leukoencephalopathy (PML). * History of cancer including hematologic malignancy and solid tumors within 10 years of screening. * Presence of other neurological disorders that could interfere with the diagnosis of MS or with the assessments of safety or efficacy during the study. * Clinically significant cardiovascular, psychiatric, pulmonary, renal, hepatic, endocrine, metabolic or gastrointestinal disease. * Any concomitant disease that may require chronic treatment with systemic corticosteroids or immunosuppressants during the course of the study. * History of alcohol or other drug abuse within 12 months prior to screening. * History of or currently active primary or secondary (non-drug-related) immunodeficiency, including known history of human immunodeficiency virus (HIV) infection. * Inability to complete an MRI scan. * Adrenocorticotropic hormone or systemic corticosteroid therapy within 4 weeks prior to screening. * Receipt of a live-attenuated vaccine within 6 weeks prior to randomization. * Any previous treatment with immunomodulatory or immunosuppressive medication without an appropriate washout period.