<p>The pursuit of sustainable, high-performance materials for next-generation technologies has accelerated the transformation of bio-based polymers, such as polylactic acid (PLA), into multifunctional platforms. This study provides a comprehensive investigation of the morphology-dependent multifunctional properties of multi-walled carbon nanotube (MWCNT)/PLA composite films. By systematically varying the MWCNT loading, the composite microstructure was precisely engineered, evolving from a phase-separated system with encapsulated nanotubes to a continuous, three-dimensional percolating network. This structural transition serves as the fundamental mechanism for modulating material performance. The incorporation of MWCNTs not only substantially enhanced the thermal stability of PLA but also led to a sharp reduction in electrical resistance. Furthermore, the linear correlation between the intensity of characteristic Raman peaks and MWCNT content facilitates quantitative analysis and spatial mapping of CNT distribution within the composites. Surface wettability exhibited a non-monotonic dependence on filler concentration, with an optimal formulation (19.5 wt% MWCNTs) demonstrating a stable hydrophobic state and remarkable dynamic stability. This integrated analysis reveals that the thermal, electrical, wetting, and spectroscopic properties are synergistically governed by the evolving nanocomposite architecture, positioning MWCNT/PLA composites as promising and designable materials for advanced applications such as functional sensors, selective separation membranes, and smart protective coatings.</p> Graphical abstract <p></p>