Chronic illnesses, such as diabetes, cardiovascular disease, and autoimmune disorders, are often accompanied by physical symptoms and psychological distress that adversely affect patients’ quality of life. This study investigates the role of Cognitive-Behavioural Therapy (CBT) in reducing these physical symptoms by addressing associated psychological stressors. The study adopt Quasi-Experiment research design, the population of the study are individual diagnosed with chronic illnesses in Lagos state, sample size of 120 participants selected using purposive sampling techniques. The CBT intervention focused on stress management, restructuring maladaptive thoughts, and developing coping skills aimed at alleviating anxiety, depression, and perceived stress. Physical symptoms, including fatigue, pain, and inflammation markers, were assessed pre- and post-intervention using standardized questionnaires which are Perceived Stress Scale (PSS) and Chronic Illness Therapy Scale (FACIT-F), data collected was analyzed using descriptive statistics and Paired t-test. Findings showed that participants in the CBT group experienced significant reductions in both physical symptoms and psychological distress compared to the control group, with improvements in stress regulation and emotional resilience closely linked to improved physical outcomes. The study concluded that CBT is an effective intervention for managing the physical symptoms of chronic illness, likely due to its impact on reducing psychological stress and enhancing adaptive coping skills. It was recommended that Integrating CBT into chronic illness care, as mental health interventions can meaningfully improve physical health outcomes.