This article deals with a problem of magneto-thermoelastic interactions in a transversely isotropic hollow cylinder due to thermal shock in the context of three-phase-lag theory of generalized thermoelasticity. The governing equations of generalized thermoelasticity of the above model under the influence of a magnetic field are established. The Laplace transform method has been used to transform the equation into the space domain, where the Galerkin finite element technique has been employed to solve the resulting equations in the transformed domain. The inversion of the Laplace transformation is done by applying a method of Bellman et al. The stresses and temperature distributions have been computed numerically and presented graphically in a numbers of figures. A comparison of the results for different theories (GN-III and 3P models) are presented and the effect of magnetic field is discussed. The results for an isotropic material (Cu) have been deduced numerically and presented graphically to compare with those of transversely isotropic material (Mg).