A Study of Guselkumab in Pediatric Participants With Moderately to Severely Active Ulcerative Colitis

Inclusion Criteria: * Weight greater than or equal to (\>=) 10 kilogram (kg) at the time of consent for screening * A pathology report to support a documented diagnosis of Ulcerative Colitis (UC) must be available in the source documents. There is no maximum duration for which a participant needs to be diagnosed with UC. If the pathology report to support a documented diagnosis of UC is not available in the source documents, the screening endoscopy with biopsies (obtained within 3 weeks before first study intervention administration) needs to support the diagnosis of UC. * Moderately to severely active UC, defined by a baseline modified Mayo (without physician's global assessment) score of 5 through 9 inclusive, with a screening Mayo endoscopy subscore \>= 2 as determined by a central review of the video of the endoscopy * Medically stable based on physical examination, medical history, and vital signs, performed at screening. Any abnormalities must be consistent with the underlying illness in the study population and this determination must be recorded in the participant's source documents and acknowledged by the investigator * Participants must have had an inadequate response and/or intolerance to biologic therapy and/or conventional therapies or be dependent upon corticosteroids Exclusion Criteria: * Have UC limited to the rectum only or to less than (\<) 20 centimeter of the colon * Presence of a stoma * Has had any kind of bowel resection within 6 months or any other intra-abdominal surgery within 3 months of baseline * Have severe colitis or have evidence of Crohn's Disease (CD)