Background: Cyclosporine is currently recommended as a third-line therapy for chronic spontaneous urticaria (CSU), while narrowband ultraviolet B (NB-UVB) phototherapy has shown promise. Objective: To compare the efficacy and safety of NB-UVB phototherapy versus cyclosporine in antihistamine-refractory CSU. Methods: This randomized, prospective, non-inferiority study recruited 50 patients with antihistamine-refractory CSU. Participants received either NB-UVB (thrice weekly) or cyclosporine (3 mg/kg/day) for 90 days alongside maximum-regulated doses of antihistamines, with a post-treatment follow-up of 90 days. Primary outcome was the Urticaria Activity Score over 7 days (UAS7), with secondary outcomes including Urticaria Control Test (UCT), Chronic Urticaria Quality of Life (CU-QoL), and biomarkers such as IL-6 and IL-31. Results: Both treatments significantly reduced UAS7 by day 15. NB-UVB provided sustained symptom control post-treatment, while cyclosporine achieved rapid relief but led to rebound flares upon discontinuation. The non-inferiority test showed that NB-UVB was not significantly worse than cyclosporine for UAS7 reduction. Both therapies reduced serum IgE, with IL-6 and IL-31 significantly decreasing in the cyclosporine group. Limitations: Single-center design, short follow-up duration. Conclusions: NB-UVB phototherapy is an effective and well-tolerated alternative to cyclosporine for antihistamine-refractory CSU, offering sustained disease suppression post-treatment. Further research is needed to explore long-term outcomes and broader applicability. Trial Registration: Clinical Trials Registry of India (CTRI/2022/11/047799).