Background: The burden attributable to late-life depression is set to increase with the ageing population. The size of the workforce trained to deliver psychogeriatric medicine is limited. Internet-delivered cognitive behavioral therapy (iCBT) is an efficacious and scalable treatment option for depression. Yet older adults are underrepresented in iCBT research. This study examines the effects of iCBT for depression across the adult lifespan among patients seeking help in routine clinical care (N = 1288). Methods: Regression analyses were used to examine the relationship between age group (e.g., 18-24years (n = 141); 25-34years (n = 289); 35-44years (n = 320); 45-54years (n = 289); 55-64years (n = 180); 65 +years (n = 69)) and presenting demographic and clinical characteristics, adherence to treatment, and rates of remission, recovery and reliable improvement. Linear mixed models were used to examine whether reductions in symptom severity, distress and impairment varied as a function of age. Results: Patients aged 65+ years were more likely to be male compared to those aged 18–34 years and have been prescribed iCBT by their GP compared to those aged 55–64 years. Patients experiencing late-life depression experienced moderate to large effect size reductions in depressive symptom severity, psychological distress, and impairment, as did all other age groups. Rates of remission, recovery or reliable improvement were comparable across the adult lifespan. Conclusions: iCBT is an effective treatment option for depression including in later life, and can be used to scale evidenced-based medicine in routine clinical care. Limitations: No follow-up data were collected. The long-term effects of treatment, particularly for those who did not experience remission, are unclear.