The aim of the present paper is to investigate the influences of the hydrostatic initial stress and the gravity field on the plane waves in a fiber-reinforced magnetothermoelastic isotropic medium using the Lord-Shulman model of generalized thermoelasticity with one relaxation time. The problem has been solved numerically using the normal mode analysis together with the eigenvalue approach. Numerical results for temperature, the displacement components, and the stresses are represented graphically, and the results are analyzed. The graphical results indicate that the effects of the hydrostatic initial stress, gravity field, and the magnetic field on plane waves in the fiber-reinforced thermoelastic medium are very pronounced. Comparisons are made to results in the absence of the hydrostatic initial stress, gravity field, and the magnetic field. Such problems are very important in many dynamical systems.