Oxidative stress, where there is an imbalance between the production of reactive oxygen species (ROS) and the body’s antioxidant defenses, is a key contributor to the pathophysiology of many chronic diseases. This process is involved in cellular injury, inflammation, and dysfunction, which are typical of diseases like cardiovascular disease, diabetes, neurodegenerative disorders, and cancer. Under these circumstances, prolonged oxidative stress drives the development of tissue injury, amplifies inflammatory reactions, and modifies cellular signal transduction. In addition to causing DNA damage and protein oxidation, oxidative stress also impacts lipid metabolism, which leads to atherosclerotic plaque formation and insulin resistance. The resultant effects of cumulative oxidative damage induce the modification of normal physiological mechanisms and the establishment of disease processes. This review discusses the pathways through which oxidative stress promotes the pathophysiology of chronic diseases and identifies potential therapeutic interventions, such as antioxidant therapies and lifestyle modifications, to reduce oxidative damage and enhance disease outcomes. The connection between oxidative stress and chronic diseases offers insights into new preventative and treatment strategies for controlling these ubiquitous health disorders.