Large-format additive manufacturing (LFAM) is used to print large-scale polymer structures. An understanding of the thermal and mechanical properties of polymers suitable for large-scale extrusion is needed for de-sign and production capabilities. An in-house-built LFAM printer was used to print polyethylene terephthalate glycol with 30% short carbon fiber (PETG CF30%) samples for thermomechanical characterization. Thermogravimetric analysis confirmed the samples had 30% carbon fiber by weight. X-ray microscopy and porosity studies found 25% porosity for undried material and 1.63% porosity for dry material. Differential scanning calorimetry showed a glass transition temperature (Tg) of 66°C, while dynamic mechanical analysis found Tg to be 82°C. The rheology indicated that PETG CF30% is a good printing material at 220°C–250°C. Bending experiments showed an average of 48.5 megapascals (MPa) for flexural strength, while tensile experiments found an average tensile strength of 25.0 MPa at room temperature. Comparison with the literature demonstrated that the 3D-printed PETG CF30% had a high Young’s modulus and was of similar tensile strength. For design purposes, prints from LFAM should be considered from a bead–layer–part standpoint. For testing purposes, both material choice and print parameters should be considered, especially when considering large layer heights.