Fused-filament-fabrication (FFF) is a commonly used and commercially successful additive-manufacturing method for thermoplastics. Depending on the FFF process parameters, the internal-strains along print direction, thermal-gradient across layers, and anisotropy introduced during layer-by-layer build-up can significantly affect the macroscopic properties, dimensional stability, and structural performance of the final part. Conversely, these factors can be optimized to result in unique, controllable thermally actuated shape-transformations. This work aims at quantifying and understanding the underlying mechanisms that drive the thermally actuated shape-transformation in three commonly used thermoplastics fabricated by the FFF method namely, poly-lactic-acid (PLA), high-impact-polystyrene (HIPS), and acrylonitrile-butadiene-styrene (ABS). Initially, the release of internal-strains is analyzed for unidirectionally printed samples experimentally and computationally, employing a thermoviscoelastic-viscoplastic constitutive model. Subsequently, two basic initial (as-printed) configurations, namely, a beam and a circular-disc are chosen to study the 1D to 2D and 2D to 3D shape-transformations, respectively. The effect of process parameters such as the printing speed, print path, and infill density on the shape transformation behavior is investigated systematically. Finally, the results are applied to demonstrate shape-transformations for application in morphing-structures and/or as an alternative, simplified process in fabricating curved-components.