The main inclusion criteria include but are not limited to the following:

• Has had ulcerative colitis (UC) (from onset of symptoms) for at least 3 months before Randomization
• Has moderately to severely active UC
• Has a weight ≥40 kg
• Satisfies at least 1 of the criteria: Has had an inadequate response or loss of response to 1 or more protocol-specified treatments; protocol specified corticosteroid dependence; has been intolerant to 1 or more protocol-specified UC treatments
• Is on treatment with any protocol-specified drugs during the study and meets drug stabilization requirements, as applicable

The main exclusion criteria include but are not limited to the following:

• Has a diagnosis of Crohn's Disease (CD) or indeterminate colitis (inflammatory bowel disease (IBD)-undefined) or other types of colitis or enteritis that may confound efficacy assessment
• Has a current diagnosis of fulminant colitis and/or toxic megacolon
• Has UC limited to the rectum
• Has a current or impending need for colostomy or ileostomy
• Has had a total proctocolectomy or partial colectomy
• Has UC exacerbation requiring hospitalization within 2 weeks before Screening
• Has any active infection as specified in the protocol
• Is known to be infected with hepatitis B virus (HBV), hepatitis C virus (HCV), or human immunodeficiency virus (HIV)
• Has evidence of active tuberculosis (TB) or meets TB exclusionary parameters
• Has a history of cancer (except fully treated nonmelanoma skin cell cancers or cervical carcinoma in situ after complete surgical removal) and is disease free for <5 years before Randomization or has a history of colorectal cancer at any time
• Has prior or current evidence of definite colonic dysplasia except for low-grade dysplasia that has been completely removed
• Has had major surgery within 3 months before Screening or has a major surgery (ie, surgical procedure requiring general anesthesia) planned during the study
• Has received protocol-specified prohibited medications

History of severe allergic reactions to study medication Currently pregnant or breastfeeding Recent participation in another clinical trial within the last 30 days Presence of uncontrolled medical conditions that could affect safety