• Has a confirmed diagnosis of UC established at least 3 months prior to screening, by clinical and endoscopic evidence and corroborated by a histopathology report.

• Has moderately to severely active UC as determined by a complete Mayo score \[including physician's global assessment (PGA)\] of 6 to 12 with a rectal bleeding subscore ≥1 and a centrally assessed endoscopic subscore ≥2 at screening.

• Has evidence of UC extending proximally to the rectum \[≥15 centimeter (cm) of involved colon\].

• Participants with extensive colitis or pancolitis of \>8 years duration or left sided colitis \>12 years duration must have documented evidence that a surveillance colonoscopy was performed within 12 months of the initial screening visit.

• Participants with a family history of colorectal cancer, personal history of increased colorectal cancer risk, age \>50 years, or other known risk factors must be up to date on colorectal cancer surveillance.

• Has demonstrated an inadequate response to, loss of response to, or intolerance to at least 1, but no more than 2 TNFα antagonists. Participants without prior failure or intolerance to biologics are not eligible. Participants who discontinued TNFα antagonist therapy for reasons other than failure or intolerance (eg, pregnancy) may be eligible after discussion with the medical monitor.

• Note: After the interim analysis, participants with inadequate response, loss of response, or intolerance to conventional UC therapy without prior exposure to biologics may be enrolled if deemed appropriate. Participants who discontinued biologics for reasons other than failure or intolerance (eg, pregnancy) may be eligible after discussion with the Medical Monitor.

• If using corticosteroids must be on a stable dose of oral corticosteroids up to a maximum of 40 mg daily of prednisone or 9 mg daily of budesonide, or equivalent for at least 2 weeks prior to screening endoscopy and must be willing to follow a mandatory taper of corticosteroids from enrollment.