<p>Functionally graded saturated porous (FGSP) plates are increasingly employed in aerospace, marine, and energy systems where components are simultaneously exposed to mechanical loading, elevated temperatures, and fluid–structure interaction. This study investigates the coupled thermo-poro-mechanical nonlinear dynamic behavior of FGSP plates resting on a Pasternak elastic foundation, aiming to address the lack of analytical frameworks capable of capturing combined thermal fields, pore-fluid effects, and geometric nonlinearity in such layered structures. The governing equations are derived using Reddy’s third-order shear deformation theory (TSDT) and the Rayleigh–Ritz energy method, while Biot’s poro-elasticity theory is incorporated to represent fluid pressure in undrained pores. Nonlinear temperature gradients through the thickness are obtained from steady-state heat conduction, and von Kármán’s assumptions are adopted to account for large deflections. The nonlinear dynamic response is evaluated using the Newmark time integration scheme with Newton–Raphson iterations. Parametric studies reveal that pore-fluid pressure, temperature rise, and foundation stiffness significantly alter dynamic stiffness and resonance characteristics, and that boundary conditions strongly govern this sensitivity. The results provide new insights into the coupled thermo-poro-mechanical behavior of FGP structures, serving as a valuable reference for engineering applications in extreme environments.</p>