One of the most important learning outcomes is to achieve the critical thinking ability of every level of learners. It is a universal phenomenon that impacts the holistic development of any nation in fast-growing technologically advanced societies. Critical thinking skill helps judgmental decision-making and justifiable problem-solving which is mandatory to survive in the unpredicted, uncertain challenges yet to come in the century. At present, Sri Lanka faces multiple types of social and economic issues which hindered the development growth of all aspects. Decision-making and problem-solving strategies of the majority population are not viable, and the same is the result of poor outcomes achieved in critical thinking skills through education. The purpose of this study is to understand the extent of the application of critical thinking skills by the secondary learners of Sri Lankan government schools since the twenty-first century skills are yet in the process of inclusion in the national curriculum. A quantitative survey method with a questionnaire among 100 secondary learners was administered to gather data. The test consists of 25 items, the results of which allow assessing critical thinking in 6 scales: remembering, understanding, applying, analyzing, evaluating, and creating. The tool also allows checking the overall score. The findings indicate considerably a lower rate of application of critical thinking skills in analytical decision-making in everyday activities. The final outcomes of the research will be helpful for curriculum designers and policy planners to implement strategic-level inclusions in the education system which at present is in the revised process.