The tension between national security and civil liberties remains a defining constitutional challenge of the twenty-first century, intensified by terrorism, cyber threats, and global crises. This study employs a mixed-methods approach, combining comparative legal analysis, empirical data collection, and statistical modeling, to examine how constitutional systems reconcile security imperatives with democratic rights. Comparative analysis of frameworks from the United States, the European Union, Pakistan, and Poland identifies variations in judicial oversight, legislative design, and executive accountability. Empirical data were gathered through surveys of 1,200 participants and 60 semi-structured interviews with legal experts and policymakers to capture public and institutional perspectives on liberty–security trade-offs. A theoretical model of proportionality is developed to quantify the balance between security measures, judicial review, threat severity, and their impact on civil rights. Regression analysis validates this model and demonstrates the strong judicial scrutiny and proportional legislative mechanisms significantly enhance constitutional balance. The findings underscore that adaptive constitutional systems, grounded in transparency, proportionality, and accountability, are more resilient in safeguarding both security and fundamental freedoms in evolving global contexts.