3D-printed carbon fiber-reinforced plastic (CFRP) has excellent qualities; yet there is a lack of study on the endurance of these parts, which makes their practical application challenging. In order to evaluate the performance of FDM-printed polymers for structural applications, understanding the underlying mechanism of fatigue is essential. However, comprehensive study on the fatigue behavior of FDM-printed polymeric materials is missing. In this study, we examine the fatigue characteristics of 3D-printed continuous fiber-reinforced Onyx composites. The experiments are conducted on composite samples fabricated using different sets of 3D printing parameters. In this study, a Markforged × 7 FDM-based 3D printer is used to fabricate the composite specimen. Composites are fabricated using Markforged flagship material Onyx as the polymer matrix and carbon fiber as the reinforcement material. Four different 3D printing parameters are used as varying input parameters for the fabrication of composite specimens, namely (a) fiber orientation, (b) layup sequence, (c) infill density, and (d) infill geometry. For fatigue fracture testing, different fatigue loadings such as 50%, 60%, and 70% of the ultimate tensile strength of the respective composite are applied and the fatigue life of each composite is evaluated. The study shows that triangle infill geometry, 50% infill density, 45° fiber orientation, and concentrated stacking of carbon fiber is the optimal condition for fatigue performance.