A Study to Evaluate the Efficacy and Safety of Bimekizumab in Adult Subjects With Moderate to Severe Chronic Plaque Psoriasis

Inclusion Criteria: Treatment Period (open-label) * Subject is considered reliable and capable of adhering to the protocol (eg, able to understand and complete diaries), visit schedule, and medication intake according to the judgment of the Investigator * Subject completes the feeder study (PS0008 \[NCT03412747\], PS0009 \[NCT03370133\], PS0013 \[NCT03410992\]) without meeting any withdrawal criteria * Female subjects must be: 1. Postmenopausal: Menopause is defined as 12 consecutive months of amenorrhea, for which there is no other obvious pathological or physiological cause 2. Permanently sterilized (eg, tubal occlusion, hysterectomy, bilateral salpingectomy) 3. Or, if of childbearing potential (and engaged in sexual activity that could result in procreation), must be willing to use a highly effective method of contraception throughout the duration of the study until 20 weeks after last administration of investigational medicinal product (IMP), and have a negative pregnancy test at the feeder study in final visit/Baseline visit in PS0014 OLE2 Period (USA and Canada) * Completed the OLE Period without meeting any withdrawal criteria * Compliant with ongoing clinical study requirements * Female subject of childbearing potential must be willing to use highly effective method of contraception * Subjects with a diagnosis of Crohn's disease or ulcerative colitis are allowed as long as they have no active symptomatic disease (US only) * Signed a separate OLE2 Period ICF Exclusion Criteria: Treatment Period (open-label) * Subject has previously participated in this study * Female subjects who plan to become pregnant during the study or within 20 weeks following last dose of study medication * Subject has any medical or psychiatric condition that, in the opinion of the Investigator, could jeopardize or would compromise the subject's ability to participate in this study. Note: For any subject with an ongoing Serious Adverse Event (SAE), or a history of serious infections in the feeder study, the Medical Monitor must be consulted prior to the subject's entry into PS0014, although the decision on whether to enroll the subject remains with the Investigator * Subject has a positive or indeterminate interferon gamma release assay (IGRA) in a feeder study, unless appropriately evaluated and treated * Subject may not participate in another study of a medicinal product or device under investigation other than the substudy * Subject has a history of chronic alcohol or drug abuse within 6 months prior to Baseline as assessed by medical history, site interview, and/or results of the specified urine drug screen OLE2 Period (USA and Canada) * Subject has developed any medical or psychiatric condition, which, in the Investigator's judgment, would make the subject unsuitable for inclusion in OLE2 Period * Subject had a positive or indeterminate interferon-gamma release assay (IGRA) in the OLE study to Week 144, unless appropriately evaluated and treated * Presence of active suicidal ideation or severe depression * Subject has developed any active malignancy or history of malignancy prior to the OLE2 Screening Visit EXCEPT treated and considered cured cutaneous squamous or basal cell carcinoma, or in situ cervical cancer