In this paper, we report on the development and the implementation of the mesoscopic approach based on the Lattice Boltzmann method (LBM) in order to simulate three-dimensional coupled modes of thermal and fluid flows. First the lattice Boltzmann method (LBM) has been used to solve transient heat conduction problems in 3D Cartesian geometries. To study the suitability of the LBM, the problem has also been extended to deal with a coupled conduction-radiation heat transfer problem in a three-dimensional cavity containing an absorbing, emitting, and scattering medium. In this case, the radiative information is obtained by solving the radiative transfer equation (RTE) using the control volume finite element method (CVFEM). Second, a 3D incompressible thermal lattice Boltzmann model is proposed to solve 3D incompressible thermal flow problems. A D3Q19 particle velocity model is incorporated in our thermal model where the density, velocity, and temperature fields are calculated using the two double population lattice Boltzmann equation (LBE). It is indicated that the present thermal model is simple and easy for implementation. It is validated by its application to simulate the 3D natural convection of fluid in a cubical enclosure, which is heated differentially at two vertical side walls. In order to test the efficiency of the developed method, comparisons are made for the effect of Rayleigh number on the temperature and velocity distributions in the medium. Validation and the analysis of numerical results of flow and thermal fields in the cubic cavity are at Rayleigh numbers of 103–106. In all studied cases, it is found that the numerical results agree well with the results reported in previous studies. The 3D LBGK algorithm presented here can also be extended for a convective radiative problem in a three-dimensional grey participating medium in the presence of computers with sufficient memory and computational power to perform well-resolved calculations of the hybrid 3D-proposed model.