Glass fiber-reinforced polyphthalamide (PPA) composites combine the robust properties of PPA with the strength and stiffness imparted by glass fibers. This work proposed a meso-scale modelling approach to predict the thermo-mechanical properties of short glass fibers reinforced polyphthalamide matrix (PPA). The proposed computational model is capable of predicting the thermo-mechanical properties of composite structures with matrix-fiber volume fraction over the temperature variations. The proposed model is validated with existing literature and further extended to parametric studies. After defining the characteristics, mixing, and microstructure of the two materials (phases), a representative volume element (RVE) is created with three different fiber orientations: 0, 45, and 90°. A complex optimization procedure is involved in the impacts of glass fiber volume fraction in polyphthalamide composites at different temperatures ranging between 0 and 60 °C. Additionally, for a large range of volume percent across temperature variation, the elastic properties are also predicted. From the presented numerical cases, the fiber volume fraction and temperature fluctuations show a substantial impact on the elastic characteristics of glass fiber polyphthalamide composites used in maritime applications.