A Study of the Efficacy and Safety of Upadacitinib (ABT-494) in Participants With Moderately to Severely Active Crohn's Disease Who Have Inadequately Responded to or Are Intolerant to Biologic Therapy

* Confirmed diagnosis of CD for at least 3 months prior to Baseline. * Confirmed diagnosis of moderate to severe CD as assessed by stool frequency (SF), abdominal pain (AP) score. * Evidence of mucosal inflammation based on the Simplified Endoscopic Score for Crohn's disease (SES-CD) on an endoscopy confirmed by a central reader. * Demonstrated an inadequate response or intolerance to any biologic therapy for infliximab, adalimumab, certolizumab pegol, vedolizumab, and ustekinumab. * If female, participant must meet the contraception recommendations.

* Participant with a current diagnosis of ulcerative colitis or indeterminate colitis. * Participant not on stable doses of CD related antibiotics, oral aminosalicylates, corticosteroids or methotrexate (MTX). * Participant with the following ongoing known complications of CD: abscess (abdominal or peri-anal), symptomatic bowel strictures, fulminant colitis, toxic megacolon, or any other manifestation that might require surgery while enrolled in the study. * Participant with ostomy or ileoanal pouch. * Participant diagnosed with conditions that could interfere with drug absorption including but not limited to short gut or short bowel syndrome. * Screening laboratory and other protocol pre-specified analyses show abnormal results.