Aerospace structures are often subjected to combined mechanical loads and temperature variations. Under constraints from structural continuity and joints, restrained thermal expansion generates additional thermal stresses, affecting deformation, stability, and failure risk. Reliable thermo-mechanical coupled analysis and topology optimization are therefore essential. However, many existing approaches rely on body-fitted discretizations, which incur high remeshing costs and mesh-dependent errors as boundaries evolve, and they may suffer from numerical diffusion and inconsistent sensitivities associated with thermally induced loads, leading to unstable convergence and reduced design reliability. This paper presents a thermo-mechanical topology optimization framework that integrates CutFEM-based coupled finite element analysis with MMC explicit geometry parameterization. Compliance is minimized under a prescribed volume-fraction constraint to study optimal material layouts in the presence of thermal loads. Complex boundaries are accurately captured on a fixed background mesh via cut-element subdomain integration and stabilization, enabling boundary evolution during optimization without remeshing. The sensitivity analysis consistently incorporates the effects of the design-dependent temperature field and equivalent thermal loads induced by thermal expansion on both the objective and constraints, improving the robustness of gradient-based updates. Numerical examples show that, compared with conventional density-based methods coupled with body-fitted FEM, the proposed approach produces designs with sharper boundaries, reduced numerical diffusion, and improved objective performance under identical settings, while exhibiting enhanced mesh independence and convergence stability. The method remains robust as thermal effects become more influential. Overall, the proposed CutFEM–MMC framework offers a high-fidelity and practically implementable route for lightweight design and reliability assessment of aerospace components under thermo-mechanical coupling.