Abstract Objectives The primary endpoint of the pivotal phase III study of infliximab (IFX) s.c. demonstrated non-inferiority of s.c. to i.v. IFX, based on 28-joint DAS-CRP (DAS28-CRP) improvement at week (W) 22 (NCT03147248). This post-hoc analysis investigated whether numerical differences in efficacy outcomes at W30/54 were statistically significant, using conservative imputation methods. Methods Patients with active RA and inadequate response to MTX received IFX i.v. 3 mg/kg at W0 and W2 (induction) and were randomized (1:1) to IFX s.c. 120 mg every 2 weeks or i.v. 3 mg/kg every 8 weeks thereafter (maintenance). Patients randomized to IFX i.v. switched to IFX s.c. from W30–54. This post-hoc analysis compared efficacy outcomes for s.c. and i.v. groups pre-switch (W30) and post-switch (W54) using last observation carried forward (LOCF) and non-responder imputation (NRI) methods. Results Of 343 randomized patients, 165 (IFX s.c.) and 174 (IFX i.v.) were analysed. At W30, significantly improved outcomes were identified with s.c. vs i.v. IFX for DAS28-CRP/DAS28-ESR/Clinical Disease Activity Index (CDAI)/Simplified Disease Activity Index (SDAI) scores (LOCF); ACR/good EULAR responses, DAS28-CRP/Boolean remission, and DAS28-CRP/DAS28-ESR/CDAI/SDAI low disease activity and remission (LOCF and/or NRI); and minimal clinically important difference in HAQ score (LOCF and NRI). After switching to IFX s.c. from IFX i.v., fewer significant between-group differences were identified at W54. Conclusion IFX s.c. showed improved efficacy at W30 compared with IFX i.v., and the reduced between-group difference in efficacy outcomes at W54 after switching supports the results suggesting benefits of IFX s.c. compared with IFX i.v. at W30. Trial registration ClincialTrials.gov, http://clinicaltrials.gov, NCT03147248, https://clinicaltrials.gov/ct2/show/NCT03147248.