Objective: The aim of this study was to investigate long-term clinical outcomes of extended treatment with CT-P10, a rituximab biosimilar, compared with rituximab reference products sourced from the USA and the EU (US-RTX and EU-RTX) in rheumatoid arthritis (RA) for up to 48 weeks. Methods: In this multinational, randomized, double-blind trial, adults with active RA received up to two courses of CT-P10, US-RTX, or EU-RTX alongside methotrexate. Efficacy endpoints included Disease Activity Score 28-joint count (DAS28) and American College of Rheumatology (ACR) response rates. Pharmacokinetics, pharmacodynamics, immunogenicity, and safety were also assessed. Results: Of 372 patients randomized to the study drug, 330 (88.7%) completed the second treatment course. Mean change from baseline to week 48 in DAS28-C-reactive protein was comparable in the CT-P10 and combined rituximab (US-RTX and EU-RTX) groups (− 2.7 and − 2.6, respectively). ACR20, ACR50, and ACR70 response rates at week 48 indicated no differences between groups (80.6%, 55.4%, and 31.7% vs. 79.8%, 53.9%, and 33.7% in the CT-P10 and combined rituximab groups, respectively). Similar improvements in the Health Assessment Questionnaire Disability Index and all medical outcomes in the Short Form 36-Item Health Survey, including physical and mental health, were seen in all groups. At week 48, antidrug antibodies were detected in 4.9%, 9.4%, and 8.6% of patients in the CT-P10, US-RTX, and EU-RTX groups, respectively. CT-P10 and rituximab displayed similar pharmacokinetic, pharmacodynamic, and safety profiles. Conclusion: CT-P10 was similar to EU-RTX and US-RTX in terms of efficacy, pharmacokinetics, pharmacodynamics, immunogenicity, and safety up to week 48.