The increasing accumulation of polyethylene terephthalate (PET) waste has created significant environmental challenges and motivated the search for sustainable recycling strategies in pavement engineering. While recycled PET has been widely investigated in hot-mix asphalt, its application in cold-mix asphalt (CMA) remains limited because of the distinct curing mechanisms and emulsion-based binder systems involved. This study presents a comprehensive experimental investigation of recycled PET-modified CMA, integrating mechanical performance evaluation, fracture characterization, microstructural analysis, and preliminary illustrative economic and environmental screening. Recycled PET particles obtained from post-consumer plastic bottles were incorporated into CMA mixtures at contents ranging from 0 to 10% by aggregate mass using the dry process. The mixtures were evaluated using Marshall stability, indirect tensile strength (ITS), moisture susceptibility, Hamburg Wheel Tracking, Semi-Circular Bend (SCB) fracture testing, stress–strain analysis, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The results showed that PET significantly enhanced the mechanical and durability performance of CMA mixtures. Marshall stability increased from 6.40 kN for the control mixture to 16.07 kN at 6% PET, while maximum ITS, tensile strength ratio, and fracture resistance were achieved at 8% PET. SEM analysis revealed a denser and more homogeneous microstructure at moderate PET contents, whereas FTIR confirmed that the PET–binder interaction was predominantly physical in nature. However, excessive PET content increased the mixture stiffness and reduced the deformability. Overall, PET contents between 6% and 8% provided an optimum balance between strength, moisture resistance, rutting resistance, and fracture performance. The findings demonstrate the potential of recycled PET as a sustainable modifier for cold-mix asphalt applications and contribute to the development of environmentally sustainable and high-performance pavement materials with improved performance. The economic and environmental screening presented is based on laboratory-scale performance indicators and simplified cost and emission factors and does not constitute a complete life-cycle assessment.