A Study to Examine the Efficacy and Safety of Zanubrutinib Given to Adults With Primary Membranous Nephropathy

Inclusion Criteria:

* Biopsy-confirmed PMN within 5 years before the initial screening (ie, the day the informed consent is signed)
* UPCR (based on 24-hour urine collection) \> 3.5 at initial screening and at confirmation assessment
* Treatment with a maximally tolerated or allowed dose of an angiotensin-converting enzyme inhibitor (ACEI) or angiotensin II receptor blocker (ARB) for ≥ 24 weeks before randomization (12 weeks before initiation of study drug for Part 1) and with adequate blood pressure control (blood pressure \< 130/80 mmHg, measured on ≥ 2 occasions \[not on the same day\] within 4 weeks before the assignment of study treatment)
* Anti-PLA2R antibody \> 50 RU/mL at confirmation assessment (Part 1 only)

Exclusion Criteria:

* Participants with a secondary cause of membranous nephropathy
* Type 1 or 2 diabetes mellitus with hemoglobin A1c (HbA1c) ≥ 7% at screening
* Severe renal disease as determined by rapid decline in eGFR (defined as \> 15 mL/min/1.73m\^2 within 24 weeks prior to randomization, not otherwise explained)
* A known history of a primary immunodeficiency or an underlying condition such as human immunodeficiency virus (HIV) infection or splenectomy that predisposes the participant to infections
* Patients at risk for tuberculosis at screening
* Known infection with serologic status reflecting active or chronic hepatitis B virus infection, or presence of hepatitis C virus antibody
* Severe hepatic insufficiency (Child-Pugh C)
* Clinically significant cardio-cerebrovascular diseases

Note: Other protocol defined Inclusion/Exclusion criteria may apply.