3D concrete printing is an advanced technology with the potential to revolutionize construction by reducing time, cost, and environmental impact compared to traditional methods. However, conventional 3D concrete printing has limitations due to the relatively low tensile strength of the printed product, making it less practical for real-world applications. Therefore, incorporating reinforcement emerges as a viable strategy to enhance the tensile strength of a 3D-printed structure. In this study, a specially designed nozzle is utilized to mitigate void formation in the printed layer during the integration of inline reinforcement. A 1.75 mm diameter high-strength polymer cable is used as reinforcement in the cementitious concrete. After printing, the cross-section of the hardened printed structure was analyzed for void formation in the printed layer. Furthermore, the printed beam’s flexural capacity and bond strength were evaluated using three-point bending and pull-out tests. In a three-point bend test, the reinforced beams exhibited a load capacity of 2671 N and a deflection of 0.38 mm; the corresponding values for cast beams were 1865 N and 0.24 mm only. This demonstrates the effectiveness of the reinforcement method using the specially designed nozzle. The pull-out test confirmed high bond strength (more than the tensile strength of the cable, which was about 64 MPa) for the 10 mm embedment length of the cable. The findings of this study are crucial for the construction sector as they highlight the highly sensitive role of the reinforcement method and nozzle design on the mechanical properties of 3D printed structures.