<p>Additive manufacturing (AM) has become a defining technology of the digital revolution, a process where a 3D model is produced layer by layer using heated material. This process has led to advancements in many fields due to the ability to create once-impossible geometries, and the use of many different materials has led to breakthroughs in a number of fields. Material extrusion (MEX) is one of the most widely used AM technologies due to its simplicity, with heated plastic extruded through a nozzle controlled by a gantry to precisely construct each layer of a desired part. Composite materials are a popular class of materials in this area, with a recent addition of carbon nanotube (CNT)-based materials allowing for increased protection from electrostatic discharge; however, little is known about this material due to its relative infancy. This study analyzes the fatigue behavior of CNT-based ABS and PETG composite polymers compared to their virgin counterparts, concluding that for the materials tested, the addition of CNTs leads to a decrease in fatigue strength and a reduced number of cycles to failure. Due to the small scale of the CNT particles compared to the polymer matrix, the CNTs serve as crack formation sites, which lead to earlier failure rather than adding strength to the material. This research provides a useful study for informing the decision-making process when using CNT-based materials in production parts.</p>