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

The primary purpose of this study is to evaluate the efficacy of guselkumab treatment in participants with active psoriatic arthritis (PsA) by assessing the reduction in signs and symptoms of PsA.

This is a study of guselkumab in participants with active PsA who are biologically naive and have had inadequate response to standard therapies. It will evaluate the clinical efficacy of guselkumab in the reduction of signs and symptoms, structural damage inhibition and the safety profile of guselkumab in the treatment of PsA. The study will consist of a screening phase (up to 6 weeks), a blinded treatment phase (approximately 100 weeks) including a placebo controlled period from Week 0 to Week 24 and an active treatment period from Week 24 to Week 100 and a safety follow-up phase of 12 weeks after the last administration of study agent. Efficacy, health economics, safety, pharmacokinetics, immunogenicity, biomarker and pharmacogenomics evaluations will be performed in the study at defined schedule.

Eligibility Criteria:
Inclusion Criteria:

* Have a diagnosis of Psoriatic Arthritis (PsA) for at least 6 months before the first administration 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 joints at screening and at baseline, and CRP greater than or equal to (\>=) 0.6 milligram per deciLitre (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 locally performed pelvic x-ray \[single anterior-posterior view\] unless a pelvic or SI joint x-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 of plaque 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 of guselkumab therapy, including but not limited to rheumatoid arthritis (RA), axial spondyloarthritis (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, 6 thioguanine, mercaptopurine, mycophenolate mofetil, hydroxyurea, tacrolimus) within 4 weeks 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 not limited to chloroquine, gold preparations, and penicillamine within 4 weeks before the first administration of study agent
* Has received apremilast within 4 weeks prior to the first administration of study agent