BACKGROUND: There is a growing armamentarium for the treatment of moderate-to-severe ulcerative colitis. We aimed to compare the relative efficacy and safety of biologics and small molecule drugs for the treatment of patients with moderate-to-severe ulcerative colitis. METHODS: In this systematic review and network meta-analysis, we searched MEDLINE, Embase, and the Cochrane Central Register of Controlled Trials without language restrictions for articles published between Jan 1, 1990, and July 1, 2021. Major congresses' databases from Jan 1, 2018, to July 3, 2021, were reviewed manually. Phase 3, placebo-controlled or head-to-head randomised controlled trials (RCTs) assessing the efficacy and safety of biologics or small molecule drugs as induction or maintenance therapies for patients with moderate-to-severe ulcerative colitis were included. Phase 2 RCTs were excluded because of their small sample sizes and inclusion of doses not further explored in phase 3 RCTs. Summary data from intention-to-treat analyses were extracted from included reports by JSL and PAO. The primary outcome was the induction of clinical remission. A network meta-analysis was done under the frequentist framework, obtaining pairwise odds ratios (ORs) and 95% CIs. The surface under the cumulative ranking (SUCRA) was used to rank the included agents for each outcome. Higher SUCRA scores correlate with better efficacy, whereas lower SUCRA scores correlate with better safety. Maintenance data on efficacy for treat-straight-through and randomised responder trials are also presented. This study is registered with PROSPERO, CRD42021225329. FINDINGS: Our search yielded 5904 results, from which 29 studies (four being head-to-head RCTs) fulfilled our inclusion criteria and were included. Of these, 23 studies assessed induction therapy with either a biologic or small molecule drug, comprising 10 061 patients with ulcerative colitis. A risk of bias assessment showed a low risk of bias for most of the included studies. Upadacitinib was significantly superior to all other interventions for the induction of clinical remission (infliximab [OR 2·70, 95% CI 1·18-6·20], adalimumab [4·64, 2·47-8·71], golimumab [3·00, 1·32-6·82], vedolizumab [3·56, 1·84-6·91], ustekinumab [2·92, 1·31-6·51], etrolizumab [4·91, 2·59-9·31], tofacitinib [2·84, 1·28-6·31], filgotinib 100 mg [6·15, 2·98-12·72], filgotinib 200 mg [4·49, 2·18-9·24], and ozanimod (2·70, 1·18-6·20), and ranked highest for the induction of clinical remission (SUCRA 0·996). No differences between active interventions were observed when assessing adverse events and serious adverse events. Vedolizumab ranked lowest for both adverse events (SUCRA 0·184) and serious adverse events (0·139), whereas upadacitinib ranked highest for adverse events (0·843) and ozanimod ranked highest for serious adverse events (0·831). INTERPRETATION: Upadacitinib was the best performing agent for the induction of clinical remission (the primary outcome) but the worst performing agent in terms of adverse events in patients with moderate-to-severe ulcerative colitis. Vedolizumab was the best performing agent for safety outcomes. With the paucity of direct comparisons in the published literature, our results might help clinicians to position drugs in treatment algorithms. FUNDING: None.