Study to Evaluate the Efficacy and Safety of Filgotinib in Participants With Active Psoriatic Arthritis Who Are Naive to Biologic DMARD Therapy

Key Inclusion Criteria:

Meet Classification Criteria for Psoriatic Arthritis (CASPAR) and have a history consistent with psoriatic arthritis (PsA) ≥ 6 months at Screening
Have active PsA defined as ≥ 3 swollen joints (from a 66 swollen joint count [SJC]) and ≥ 3 tender joints (from a 68 tender joint count [TJC]) at Screening and Day 1; these may or may not be the same joints at Screening and Day 1

Must have a documented history or active signs of at least one of the following at Screening:

Plaque psoriasis
Nail changes attributed to psoriasis
Have had inadequate response or intolerance to ≥1 conventional synthetic disease-modifying anti-rheumatic drug (csDMARD), apremilast and / or NSAID, administered over the course of ≥ 12 weeks for the treatment of PsA, as per local guidelines / standard of care

Key Exclusion Criteria:

Prior PsA or psoriasis treatment with a biologic DMARD
Prior exposure to a janus kinase (JAK) inhibitor > 2 doses
Any active / recent infection
Any chronic and / or uncontrolled medical condition that would put the individual at increased risk during study participation or circumstances which may make an individual unlikely or unable to complete or comply with study procedures and requirements, per investigator judgement
Any moderately to severely active musculoskeletal or skin disorder other than PsA or plaque psoriasis that would interfere with assessment of study parameters, as per judgement of investigator

NOTE: Prior history of reactive arthritis or axial spondyloarthritis is permitted if there is documentation of change in diagnosis to PsA or additional diagnosis of PsA

Any history of an inflammatory arthropathy with onset before age 16 years old
Active autoimmune disease that would interfere with assessment of study parameters or increase risk to the individual by participating in the study (e.g. uveitis, inflammatory bowel disease, uncontrolled thyroiditis, systemic vasculitis, transverse myelitis), per judgement of investigator
Pregnancy or nursing females
Active drug or alcohol abuse, as per judgement of investigator

Note: Other protocol defined Inclusion/Exclusion criteria may apply.