A Study Evaluating the Efficacy and Safety of Guselkumab Administered Subcutaneously in Participants With Active Psoriatic Arthritis

Inclusion Criteria:

• Have a diagnosis of Psoriatic Arthritis (PsA) for at least 6 months before the firstadministration of study agent and meet Classification criteria for Psoriatic Arthritis (CASPAR) at screening
• Have active PsA as defined by: at least 5 swollen joints and at least 5 tender jointsat screening and at baseline, and CRP greater than or equal to (>=) 0.6 milligram perdeciLitre (mg/dL) at screening from the central laboratory
• Have at least 1 of the PsA subsets: distal interphalangeal joint involvement,polyarticular arthritis with absence of rheumatoid nodules, arthritis mutilans,asymmetric peripheral arthritis, or spondylitis with peripheral arthritis (confirmation of sacroiliitis should be performed at the screening visit by a locallyperformed pelvic x-ray [single anterior-posterior view] unless a pelvic or SI jointx-ray or pelvic magnetic resonance imaging (MRI) has been previously performed.Results must be documented)
• Have active plaque psoriasis, with at least one psoriatic plaque of >= 2 centimeter (cm) diameter or nail changes consistent with psoriasis or documented history ofplaque psoriasis
• Have active PsA despite previous non-biologic disease-modifying antirheumatic drug (DMARD), apremilast, and/or nonsteroidal anti-inflammatory drug (NSAID) therapy

Exclusion Criteria:

• Has other inflammatory diseases that might confound the evaluations or benefit ofguselkumab therapy, including but not limited to rheumatoid arthritis (RA), axialspondyloarthritis (this does not include a primary diagnosis of PsA with spondylitis),systemic lupus erythematosus, or Lyme disease
• Has previously received any biologic treatment
• Has ever received tofacitinib, baricitinib, filgotinib, peficitinib (ASP015K),decernotinib (VX-509), or any other Janus kinase (JAK) inhibitor
• Has received any systemic immunosuppressants (eg, azathioprine, cyclosporine, 6thioguanine, mercaptopurine, mycophenolate mofetil, hydroxyurea, tacrolimus) within 4weeks of the first administration of study agent
• Is currently receiving 2 or more non-biologic DMARDs (other than methotrexate [MTX],sulfasalazine [SSZ], Hydroxychloroquine [HCQ], leflunomide [LEF]) including, but notlimited to chloroquine, gold preparations, and penicillamine within 4 weeks before thefirst administration of study agent
• Has received apremilast within 4 weeks prior to the first administration of studyagent