Additive manufacturing by 3D printing has emerged as a promising construction method offering numerous advantages, including reduced material usage and construction waste, faster build times, and optimized architectural forms. One area where 3D printing’s potential remains largely unexplored is in combination with lightweight materials, especially lightweight gypsum. This research paper explores the potential of combining 3D printing technology with lightweight gypsumbased composites to extend the relatively limited gypsum application possibilities in the construction industry. The study investigates the use of expanded polystyrene (EPS) beads as an aggregate in gypsum composites, focusing on the printability of the mixture and hardened state mechanical properties in various print directions. Mechanical tests reveal that 3D printing can reduce the compressive strength of the EPS–gypsum composite by between 3% and 32%, and the flexural strength by up to 22%, depending on testing direction. However, the technology opens up new production possibilities for applications where such strength can be sufficient. The study describes that a slight increase in the water-to-gypsum (W/G) ratio in 3D-printed mortars enhances homogeneity and reduces porosity, resulting in improved structural uniformity and therefore higher flexural and compressive strength values. Furthermore, the paper discusses the mechanical anisotropy observed in 3D-printed samples. The combination of 3D printing technology and lightweight gypsum offers the potential for sustainable construction practices by reusing waste materials and creating lightweight, thermally and acoustically insulative, as well as architecturally diverse building components.