The purpose of this protocol is to evaluate the efficacy of tulisokibart in participants with moderately to severely active ulcerative colitis. Study 1's primary hypotheses are that at least 1 tulisokibart dose level is superior to Placebo in the proportion of participants achieving clinical remission according to the Modified Mayo Score at Week 12, and that at least 1 tulisokibart dose level is superior to Placebo in the proportion of participants achieving clinical remission according to the Modified Mayo Score at week 52. Study 2's primary hypothesis is that at least 1 tulisokibart dose level is superior to Placebo in the proportion of participants achieving clinical remission according to the Modified Mayo Score at Week 12.