• Diagnosis must be made per Juvenile Idiopathic Arthritis (JIA) International League of Associations for Rheumatology (ILAR) diagnostic criteria and the onset of disease must have been before the participant's 16th birthday

• Failure or inadequate response to at least a 2 month course of methotrexate (MTX) before screening

• Participants must have greater than or equal to (\>=) 5 joints with active arthritis at screening and at Week 0 as defined by American College of Rheumatology (ACR) criteria (that is, a joint with either swelling, or in the absence of swelling, limited range of motion associated with pain on motion or tenderness)

• Participants must have a screening C-reactive protein (CRP) of \>=0.1 milligram (mg)/deciliter (dL) with the exception of approximately 30 percent (%) of the study population

• Participants must have active polyarticular juvenile idiopathic arthritis (pJIA) despite current use of oral, intramuscular, or subcutaneous MTX for \>=2 months before screening. For participants with body surface area (BSA) less than (\<)1.67 meter square (m\^2), the MTX dose must be between 10 to 30 milligram per meter square (mg/m\^2) per week and stable for \>=4 weeks before screening. For participants with BSA \>=1.67 m\^2, the MTX dose must be a minimum of 15 mg/week and must be stable for \>=4 weeks before screening. In situations where there is documented intolerance of doses greater than (\>)10 mg/m\^2 weekly (for participants with BSA \<1.67 m\^2) or \>=15 mg/week (for participants with BSA \>=1.67 m\^2); or where documented country or site regulations prohibit use of \>=15 mg of MTX per week in participants with BSA \>=1.67 m\^2, participants may be entered into the trial on a lower dose of MTX