This is a multicenter, open-label, intra-subject, dose escalation study to evaluate the safety, tolerability, pharmacokinetics, pharmacodynamics, and therapeutic potential of BCX10013 in participants with PNH. Approximately 8 participants will be enrolled in this study. Participants may receive treatment for up to 52 weeks.

Key Inclusion Criteria:

1. Male or non-pregnant, non-lactating female adults ≥ 18 years old.
2. Documented diagnosis of PNH confirmed by flow cytometry.
3. Body mass index (BMI) ≤ 40 kg/m^2.
4. Are either: (a) naïve to treatment with a complement inhibitor; or (b) have received no treatment with ravulizumab for at least 12 months prior to the screening visit and have received no treatment with eculizumab or pegcetacoplan for 6 months prior to the screening visit.
5. Documentation of current vaccinations against N. meningitidis, S. pneumoniae, and H. influenzae type B [Hib] or willingness to start vaccination series at least 14 days prior to Day 1.

Key Exclusion Criteria:

1. Known history of or existing diagnosis of hereditary complement deficiency.
2. History of hematopoietic cell transplant or solid organ transplant or anticipated candidate for transplantation during the study.
3. Myocardial infarction or cerebrovascular accident within 30 days prior to screening, or current and uncontrolled clinically significant cardiovascular or cerebrovascular condition, including unstable angina, severe congestive heart failure, unexplained syncope, arrhythmia, and critical aortic stenosis.
4. History of malignancy within 5 years prior to the screening visit.
5. Treatment with anti-thymocyte globulin within 180 days prior to the screening visit.
6. Initiation of treatment with an erythropoiesis-stimulating agent (eg, erythropoietin), a thrombopoietin receptor agonist (eg, eltrombopag), or danazol within 28 days prior to the screening visit.
7. Receiving iron with an unstable dose (ie, increasing or decreasing) in the 28 days prior to the screening visit.