The aim of this paper is to provide a closed-form solution for the thermal stress distribution in a rectangular metal/composite bonded joint. This distribution depends on two directions, so it is suitable for studying bidimensional structures such as metallic plates reinforced with a rectangular composite patch. The solution is obtained using Fourier series. The relevance of the approach proposed in this paper is highlighted through various examples that clearly show that some coupling effects between the two directions of the problem take place. The influence of the nature of the composite plate used is analysed and discussed.