Lung cancer (LC) remains the leading cause of cancer-related mortality worldwide, representing a major public health challenge. Although low-dose computed tomography is currently the standard screening method for high-risk individuals to reduce mortality, its clinical performance is limited by false-positive findings and restricted accessibility. Emerging biomarker-based liquid biopsy offers a promising non-invasive approach for cancer detection. This narrative review provides a critical overview and evaluation of clinically endorsed liquid biopsy applications for guiding treatment in advanced-stage lung cancer, as well as investigational advances in liquid biopsy for early cancer detection. We also address challenges of current liquid biopsy technologies, the integration of artificial intelligence, implementation improvements, and future perspectives for their adoption into routine clinical practice. To complement this narrative review, a structured search of the ClinicalTrials.gov registry was performed to identify clinical trials evaluating liquid biopsy in lung cancer. Current evidence supports the clinical use of liquid biopsy for molecular profiling and treatment selection in advanced non-small cell lung cancer (NSCLC), whereas its application in early detection, screening, and minimal residual disease (MRD)-guided management remains investigational and requires further prospective validation. Overall, liquid biopsy represents a promising complementary approach to advance precision oncology and improve lung cancer management.