Key Inclusion Criteria:  Diagnosis of PNH confirmed by high-sensitivity flow cytometry testing with PNH granulocytes described in the protocol Active disease, as defined by the presence of 1 or more PNH-related signs or symptoms described in the protocol LDH level ≥2 × ULN at the screening visit  Key Exclusion Criteria:  Prior treatment with a complement inhibitor within 6 months prior to screening visit, unless patient was treated with eculizumab or ravulizumab and has documented C5 variant R885H/C in which case there is no exclusion of such patients Receipt of an organ transplant, history of bone marrow transplantation or other hematologic transplant Body weight <40 kilograms at screening visit Planned use of any complement inhibitor therapy other than study drugs during the treatment period Not meeting meningococcal vaccination requirements for ravulizumab according to the current local prescribing information (where available) and at a minimum documentation of meningococcal vaccination within 5 years prior to screening visit Any contraindication for receiving Neisseria meningitidis vaccination Unable to take antibiotics for meningococcal prophylaxis (if required by local ravulizumab prescribing information, where available, or national guidelines/local practice or if necessary when vaccination is less than 2 weeks from study treatment initiation) Any active, ongoing infection or a recent infection requiring ongoing systemic treatment with antibiotics, antivirals, or antifungals within 2 weeks of screening or during the screening period Documented history of active, uncontrolled, ongoing systemic autoimmune diseases  Note: Other protocol-defined Inclusion/ Exclusion Criteria apply