Objectives Evaluate the efficacy and safety of the Janus kinase-1 inhibitor filgotinib in Japanese patients with rheumatoid arthritis (RA) and inadequate response to methotrexate (MTX). Methods Data from 147 Japanese patients in FINCH 1, a 52-week global Phase 3 study, were analysed up to 24 weeks. Patients received once-daily filgotinib 200 or 100 mg, biweekly adalimumab, or placebo, all with stable background MTX. Results In the Japanese population, American College of Rheumatology 20% response rates at Week 12 (primary endpoint) were 77.5%, 65.9%, 53.6%, and 36.8% for filgotinib 200 mg, filgotinib 100 mg, adalimumab, and placebo. Proportions of patients achieving Disease Activity Score with 28 joints <2.6 at Week 24: filgotinib 200 mg, 65.0%; filgotinib 100 mg, 51.2%; adalimumab, 42.9%; and placebo, 5.3%. Incidence rates of serious infections: filgotinib 200 mg, 2.5%; filgotinib 100 mg, 0%; adalimumab, 10.7%; and placebo, 5.3%. Treatment-emergent laboratory abnormalities Grade ≥3 occurred in five (12.5%) filgotinib 200 mg, three (7.3%) filgotinib 100 mg, one (3.6%) adalimumab, and no placebo patients. No deaths were reported among Japanese patients. Conclusions Filgotinib once daily combined with MTX was effective and generally safe and well tolerated up to Week 24 in Japanese patients with RA and inadequate response to MTX.