BACKGROUND: Patients with moderately to severely active ulcerative colitis have distinct filgotinib response trajectories. AIMS: Evaluate factors associated with response to filgotinib over time. METHODS: Patients from SELECTION (NCT02914522) receiving filgotinib 200 mg (FIL200) or 100 mg (FIL100), or placebo were included. Factors associated with partial Mayo Clinic Score (pMCS) were assessed post hoc using a mixed model for repeated measures (MMRM). The prognostic value of week 10 faecal calprotectin (FCP) was assessed versus week 58 outcomes; p values are nominal. RESULTS: The MMRM included 558 patients (FIL200, n = 199; FIL100, n = 172; placebo, n = 187). For filgotinib, factors associated with lower week 58 pMCS versus respective comparators (p < 0.05) included being biologic-naive, low baseline inflammatory burden (endoscopic subscore <3, C-reactive protein </=3 mg/L), or week 10 histological remission, endoscopic subscore </=1, rectal bleeding and stool frequency subscores of 0, Inflammatory Bowel Disease Questionnaire scores >170, and/or lower FCP concentration. The optimal prognostic week 10 FCP cut-off for a concurrent week 10 Mayo Clinic Score response was <250 microg/g; combined week 10 FCP <250 microg/g and pMCS remission had similar week 58 prognostic value for clinical remission as week 10 endoscopic response. CONCLUSION: Being biologic-naive, having low baseline inflammatory burden, or strong week 10 filgotinib responses were associated with lower pMCS over 1 year of treatment. FCP <250 microg/g and week 10 pMCS remission may reduce the need for follow-up endoscopy.