In this paper, we demonstrate that the standard theory of thermoelasticity fails in describing stress dependence of laser-exited ultrasound in real dielectric and especially conductive materials. A theoretical model of thermoelasticity considering the thermal perturbation of nonstationary defect states with relaxation is presented and analyzed. To explain the obtained experimental data for metals, it is necessary to also consider a change in the pressure of the electron gas due to the defect perturbation. The proposed model is used to describe linear and nonlinear behavior of the laser ultrasonic signals near a hole in a dielectric ceramic and a metal alloy submitted to a uniform compression. The model introduces an effective dynamic coefficient of thermal expansion for real stressed materials. The obtained results provide an opportunity to estimate mechanical stresses in different materials. In this paper, we describe the calibration of the laser ultrasonic signals on stress in combination with hole drilling. The approach also allows us to estimate relaxation times of the laser-excited defects in stressed materials.