Charge-density-wave (CDW) order in REPt₂Si₂ (RE = Pr, Nd) develops through a complex sequence of structural and electronic transitions. Using atomic pair distribution function analysis and large-scale structural modeling, we show that both compounds exhibit local lattice distortions dominated by locally static Pt displacements already present at room temperature, prior to the onset of long-range CDW order. Upon cooling, these distortions become progressively correlated and evolve into superstructures characterized by alternating short and long Pt–Pt distances, forming lattice modulations along different crystallographic directions. Our results suggest a predominantly order-disorder character of the higher-temperature second-order transitions, whereas the lower-temperature first-order transitions involve a significant additional displacive component, superimposed on the preexisting Pt displacements, and further reorganization of the CDW state. These findings establish a structural connection between intrinsic lattice instabilities and the development of long-range CDW order in PrPt₂Si₂ and NdPt₂Si₂.