Background: The efficacy and safety of omalizumab in patients with severe allergic asthma have been established in both randomized controlled trials and real-life studies. Objective: To evaluate the sustained effectiveness and safety of long-term treatment with omalizumab in a real-world setting. Methods: In this retrospective study, we included patients treated with omalizumab for at least 8 years in four asthma clinics in Greece. Pulmonary function, asthma control, oral corticosteroids (OCS) dose, and exacerbations were recorded before treatment, 6 months later, and annually thereafter. Adverse events were also recorded. Results: Forty-five patients (66.7% women), mean ± standard deviation (SD) age 55.3 ± 12.2 years, were included. The duration of treatment with omalizumab was 10.6 ± 1.2 years. The annual exacerbation rate decreased from 4.1 before omalizumab initiation to 1.1 after 1 year of treatment and remained low up to the 8th year of treatment (p < 0.001). From the 19 patients who were receiving OCS at baseline, 21.1% patients discontinued after 6 months, 47.4% were still on OCS after 4 years of therapy, and 31.6% were on OCS after 8 years. With regard to the OCS dose, 36.8% of the patients reduced the dose ≥ 50% after 6 months and 68.4% achieved 50% reduction after 2 years. The mean daily OCS dose before omalizumab initiation was 7.8 mg of prednisolone or the equivalent, reduced to 4.7 mg/day after 6 months, which reached 1.6 mg/day after 8 years (p < 0.001). Treatment with omalizumab resulted in significant improvements of asthma control and lung function. No severe adverse events were reported. Conclusion: In this real-life study, omalizumab resulted in significant and sustained improvements in asthma exacerbations, asthma control, and lung function, and had a steroid sparing effect and a good safety profile.