Inclusion Criteria:
* Have psoriatic arthritis (PsA) symptoms for ≥ 6 months prior to screening, as assessed by the investigator
* Have PsA on the basis of the Classification Criteria for Psoriatic Arthritis (CASPAR) with peripheral symptoms at screening visit, as assessed by the investigator
* Have ≥ 5 tender joints and ≥ 5 swollen joints at screening and randomisation visits, as assessed by the investigator
* At least one psoriasis (PsO) lesion or a documented personal history of PsO at screening, as assessed by the investigator
* If patients receive concurrent PsA treatments, these need to be on stable doses
* Active PsA that has been inadequately controlled by standard doses of non-steroidal anti-inflammatory drugs (NSAIDs) administered for ≥ 4 weeks, or traditional disease-modifying anti-rheumatic drugs (DMARDs) (including sulfasalazine) administered for ≥ 3 months, or tumor necrosis factor inhibitor (TNFi) agents, or subjects are intolerant to NSAIDs or DMARDs or tumor necrosis factor inhibitor (TNFi) agents, as assessed by the investigator
Exclusion Criteria:
* Major chronic inflammatory or connective tissue disease other than PsA (e.g. rheumatoid arthritis, systemic lupus erythematosus, ankylosing spondylitis, Lyme disease, gout) and fibromyalgia, as assessed by the investigator
* Has received any therapeutic agent directly targeted to interleukin 12/23 (IL-12/23) (including ustekinumab), IL-23 or IL-17 (including secukinumab)
* Prior use of more than two different TNFi agents
* Use of the following treatments: TNFi agents within 12 weeks, etanercept within 8 weeks, leflunomide without cholestyramine wash-out within 8 weeks, systemic non-biologic medications for psoriatic arthritis or psoriasis and photochemotherapy within 4 weeks, intraarticular injections (including steroids) and intramuscular or intravenous corticosteroid treatment within 4 weeks, topical psoriasis medications and phototherapy within 2 weeks, low and high potency opioid analgesics within 2 weeks prior to randomisation
* Plans for administration of live vaccines during the study period or within 6 weeks prior to randomisation
* History of allergy/hypersensitivity to a systemically administered biologic agent or its excipients
* Active systemic infections during the last 2 weeks (exception: common cold) prior to randomisation, as assessed by the investigator
* Chronic or relevant acute infections including HIV, viral hepatitis and (or) active tuberculosis (TB). Patients with a positive QuantiFERON TB or purified protein derivate (PPD) test may participate in the study if further work up (according to local practice/guidelines) establishes conclusively that the patient has no evidence of active TB.
* Any documented active or suspected malignancy or history of malignancy within 5 years prior to screening, except appropriately treated basal or squamous cell carcinoma of the skin or in situ carcinoma of uterine cervix
* Major surgery performed within 12 weeks prior to randomisation or planned within 32 weeks after randomisation (e.g. hip replacement, aneurysm removal, stomach ligation), as assessed by the investigator
* Total white blood count (WBC) \< 3,000/µL, or platelets \< 100,000/µL or neutrophils \< 1,500/µL, or hemoglobin \< 8.5 g/dL at screening
* Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) \> 2x the upper limit of normal, or serum direct bilirubin ≥ 1.5 mg/dL at screening
* Positive rheumatoid factor or anti-cyclic-citrullinated peptide (anti-CCP) antibodies at screening
