Objectives: Some patients with rheumatoid arthritis develop interstitial lung disease (RA-ILD) that develops into progressive pulmonary fibrosis. We assessed the efficacy and safety of nintedanib versus placebo in patients with progressive RA-ILD in the INBUILD trial. Methods: The INBUILD trial enrolled patients with fibrosing ILD (reticular abnormality with traction bronchiectasis, with or without honeycombing) on high-resolution computed tomography of >10% extent. Patients had shown progression of pulmonary fibrosis within the prior 24 months, despite management in clinical practice. Subjects were randomised to receive nintedanib or placebo. Results: In the subgroup of 89 patients with RA-ILD, the rate of decline in FVC over 52 weeks was −82.6 mL/year in the nintedanib group versus −199.3 mL/year in the placebo group (difference 116.7 mL/year [95% CI 7.4, 226.1]; nominal p = 0.037). The most frequent adverse event was diarrhoea, which was reported in 61.9% and 27.7% of patients in the nintedanib and placebo groups, respectively, over the whole trial (median exposure: 17.4 months). Adverse events led to permanent discontinuation of trial drug in 23.8% and 17.0% of subjects in the nintedanib and placebo groups, respectively. Conclusions: In the INBUILD trial, nintedanib slowed the decline in FVC in patients with progressive fibrosing RA-ILD, with adverse events that were largely manageable. The efficacy and safety of nintedanib in these patients were consistent with the overall trial population. A graphical abstract is available at: https://www.globalmedcomms.com/respiratory/INBUILD_RA-ILD . Key Points • In patients with rheumatoid arthritis and progressive pulmonary fibrosis, nintedanib reduced the rate of decline in forced vital capacity (mL/year) over 52 weeks by 59% compared with placebo. • The adverse event profile of nintedanib was consistent with that previously observed in patients with pulmonary fibrosis, characterised mainly by diarrhoea. • The effect of nintedanib on slowing decline in forced vital capacity, and its safety profile, appeared to be consistent between patients who were taking DMARDs and/or glucocorticoids at baseline and the overall population of patients with rheumatoid arthritis and progressive pulmonary fibrosis.