Objectives: To describe the long-term effectiveness and safety of certolizumab pegol in patients with moderate-to-severe rheumatoid arthritis (RA) in a real-world setting in France. Methods: ECLAIR was a 3-year longitudinal, prospective, observational, multicentre study. The primary objective was to describe the EULAR response after 1 year of certolizumab pegol treatment. Other endpoints included DAS28, clinical disease activity index, health assessment questionnaire disability index, fatigue assessment scale, patient's assessment of arthritis pain, patient and physician global assessments of disease activity, patient quality of life, and long-term safety. Results: A total of 792 patients were enrolled, of whom 776 comprised the safety set, and 733 the full analysis set. In the full analysis set, 559, 469 and 430 patients had a 12-, 24- and 36-month visit, respectively. This included 378, 296 and 246 patients still receiving certolizumab pegol at these visits. The percentage of EULAR responders was 75.3% (305/405 patients with an available EULAR response) at 12, 76.5% (261/341) at 24, and 79.6% (226/284) at 36 months. Among those still receiving certolizumab pegol, the percentage of EULAR responders was 81.7% (237/290) at 12, 81.1% (185/228) at 24, and 87.3% (158/181) at 36 months. Sustained improvements were observed in other effectiveness outcomes. Overall, 45.1% (350/776) of patients experienced 776 adverse drug reactions. No new safety signals were identified. Conclusions: This is the first prospective, observational study of an anti-TNF treatment in France. The results confirm the effectiveness and safety profile of certolizumab pegol treatment in patients with RA in a real-world setting.