This double-blind, randomized, placebo-controlled, multinational, multicenter, parallel-group, Phase 3, 2-arm, study will investigate the efficacy and safety of belumosudil compared with placebo, both administered on top of azithromycin and standard-of-care regimen of immunosuppression in male or female participants at least 1 year after bilateral lung transplant, who are at least 18 years of age and who have evidence of progressive CLAD despite azithromycin therapy. Study details include: The study duration will be up to 31 weeks for participants not entering the open-label extension (OLE) period and up to 57 weeks for participants entering the OLE period but not the long-term OLE. The treatment duration will be up to 26 weeks for participants not entering the OLE period and up to 52 weeks for participants entering the OLE period but not the long-term OLE. The number of visits will be up to 10 visits for participants not entering the OLE period and up to 16 visits for participants entering the OLE period but not the long-term OLE. For participants who enter the long-term OLE, treatment and study participation will continue with visits every 12 weeks per protocol specifications.