In this article, a Laguerre-based finite-element method (LBFEM) combined with domain decomposition is proposed for large-scale transient thermal simulation. The unconditionally stable marching-on-in-order scheme is obtained using the weighted Laguerre polynomials and Galerkin testing procedure to eliminate the time variable of the temperature field. An effective data filtering method is utilized to reduce the number of basis functions and improve the efficiency of simulation. To handle the large-scale problems, a domain decomposition scheme named finite element tearing and interconnecting (FETI) is applied. The entire computational domain can be divided into a series of small-scale subdomains to reduce the computational resources. Numerical results are presented to demonstrate the accuracy and efficiency of the proposed method.