Inclusion Criteria:  Male or female, aged ≥ 18 years old Body weight ≥ 40 kg Primary diagnosis of C3G, IgAN, or PMN confirmed by central pathology review An eGFR ≥ 50 mL/min/1.73 m2 (or ≥ 30 mL/min/1.73 m2 after DMC recommendation) Receiving treatment with a stable, maximum recommended or maximum tolerated dose of an angiotensin-converting enzyme inhibitor (ACEi) or angiotensin receptor blocker (ARB) for at least 60 days prior to the Day 1 Visit Documentation of current vaccinations against Neisseria meningitidis and Streptococcus pneumoniae or willingness to start vaccination series  Exclusion Criteria:  Known congenital deficiency of C1s, C1r, C1q, C2, or C4 History of hematopoietic cell transplant or solid organ transplant or anticipated candidate for transplantation Myocardial infarction or cerebrovascular accident within 30 days prior to screening, or current and uncontrolled clinically significant cardiovascular or cerebrovascular condition History of malignancy within 5 years prior to the screening visit Active serious bacterial, viral, or fungal infection or any other serious infection within 14 days of screening Treatment with any systemic immunosuppressive or immunomodulatory therapy within 90 days OR within 180 days for anti-CD20 antibody therapies (eg, rituximab) prior to the screening visit Treatment with renin inhibitors (eg, aliskiren) or sodium-glucose-cotransporter 2 (SGLT2) inhibitor within 60 days prior to Day 1