Objectives Bimekizumab, a monoclonal IgG1 antibody that selectively inhibits interleukin (IL)-17F in addition to IL-17A, has demonstrated tolerability and clinical efficacy in patients with psoriatic arthritis (PsA). Here, we report an additional year of safety and efficacy of bimekizumab to 3 years. Methods BE OPTIMAL (NCT03895203; biologic disease-modifying antirheumatic drug [bDMARD]-naïve) and BE COMPLETE (NCT03896581; prior inadequate response/intolerance to tumour necrosis factor inhibitors [TNFi-IR]) assessed subcutaneous bimekizumab 160 mg every 4 weeks in patients with PsA. Study completers could enrol in the BE VITAL open-label extension (NCT04009499). Outcomes reported as observed, or using modified non-responder or multiple imputation, to 3 years. Results Overall, 546/299 (76.7/74.8%) bDMARD-naïve/TNFi-IR patients randomised to bimekizumab or placebo at baseline (Bimekizumab Total group) completed Year 3. Treatment-emergent adverse event rates (exposure-adjusted incidence rate/100 patient-years [95% CI]) for bimekizumab-treated patients through 3 years were 164.2 (152.7−176.3) in bDMARD-naïve and 88.6 (79.1−98.9) in TNFiIR patients, consistent with those at Year 1 with no new safety signals identified. Response rates for efficacy outcomes were sustained up to 3 years; at Year 1 and Year 3 respectively, 56.1/50.4% and 53.2/55.2% of bDMARD-naïve/TNFi-IR patients achieved ACR50, 61.8/58.2% and 59.5/59.1% achieved swollen joint count resolution, and 64.7/66.2% and 61.9/67.5% had 100% improvement from baseline in Psoriasis Area and Severity Index. Responses for other efficacy measures were similarly sustained and consistent in bDMARD-naïve and TNFi-IR patients. Conclusion Bimekizumab demonstrated sustained high levels of efficacy and tolerability to 3 years, supporting its suitability for long-term treatment in bDMARD-naïve and TNFi-IR patients with PsA.