The purpose of this study is to assess how well JNJ-78934804 works (efficacy) and how safe it is (safety) as compared to guselkumab at Week 48 in participants with moderately to severely active ulcerative colitis (UC, a chronic disease of the large intestine in which the lining of the colon becomes inflamed and develops ulcers).
Diagnosis of ulcerative colitis (UC) established at least 12 weeks before screening including both endoscopic evidence and a histopathology report consistent with a diagnosis of UC.
Moderately to severely active UC defined as baseline (Week 0) modified Mayo score of 5 to 9, inclusive, using the Mayo endoscopy subscore obtained during central review of the screening video endoscopy
An endoscopy subscore >=2 as obtained during central review of the screening video endoscopy
Have had an inadequate initial response, loss of response, or intolerance to previous approved systemic therapies
Isolated proctitis (UC limited to the rectum only or to less than [<] 20 centimeter [cm] from the anal verge) as determined during central review of the screening video endoscopy OR Has a diagnosis of isolated proctitis
Diagnosis of indeterminate colitis, microscopic colitis, ischemic colitis, Crohn's colitis or any findings suggestive of CD
Has a history of or ongoing chronic or recurrent infectious disease
Has previously demonstrated inadequate initial response, loss of response, allergy, hypersensitivity or intolerance to guselkumab or to golimumab