As a building material with economic potential and various beneficial properties, glass fiber reinforced concrete (GRC) has been rapidly promoted and applied in the field of civil construction. The coefficient of thermal expansion (CTE) of fiber-reinforced composites plays a crucial role in the design and analysis of such composites. Therefore, the thermal expansion coefficient of glass fiber reinforced concrete is the focus of this paper. A micromechanics model based on the Mori–Tanaka method is proposed to predict the overall thermal expansion coefficient of GRC. The model considers concrete as a two-phase composite material composed of cement mortar and aggregate. In the derivation process, concrete is treated as the equivalent matrix while glass fiber is treated as the inclusion phase. The present analysis takes into account the effects of glass fiber aspect ratio and reinforcement direction, as well as the volume fractions of aggregate and glass fiber. It is found that the glass fiber aspect ratio and reinforcement direction have a significant effect on the thermal expansion coefficient of concrete. The advantage of this model is that it provides a simple and accurate approach for predicting the CTE of glass fiber reinforced concrete. The developed model is validated by comparison with theoretical and experimental data in the literature.